You walk in the door at 8:02 a.m. to be greeted by your secretary. She hands you a stack of 18 "While You Were Out" slips that she has transcribed from your voicemail. You glance at your overstuffed briefcase in one hand, your laptop in the other, and the stack of folders under your arm. You consider trying to squeeze the messages between two available fingers. "Oh, wait," she says, and she points to three Federal Express packages. No way to carry it all now, so you head off to unload the work you brought back from home.

Your desk looks like a war zone—and your side lost. A quick glance at your computer reminds you to check your e-mail. What? 26 messages! How can that be? You checked it before you went to bed last night and spent 45 minutes answering all the messages. As you read your e-mail, you flip through yesterday's mail. The phone rings, and as you half-listen to one of your employees you scroll through your e-mail to decide what to answer now and what can wait until later.

Your day has just begun, and already you are exhausted. You feel like an octopus, with your arms and brain moving in multiple directions at the same time. By the time you have finished your work day—technically eight hours later (ha!)—you will have started and stopped dozens of tasks. The phone, the fax, the beep of an incoming e-mail all wrench your mind from what you are doing and thinking. When you finally return to your work, often you have lost your train of thought. Finding it again takes extra effort and time that you don't really have.

You're not alone. A study by the Institute for the Future reported that employees of Fortune 1,000 companies send and receive 178 messages a day and are interrupted an average of at least three times an hour. No doubt, the more senior the executive, the worse the problem. One East Coast executive with whom we consulted found communications technologies so distracting that he had to arrive at the office in the early hours of the morning to get anything done. Even then, he had to hide in a room far away from the beeping fax machine and from any e-mail hookup.

This problem is what we call "Multitasking Madness." Human beings have brains that allow them to appear as though they can comfortably perform more than one task at a time. In reality, our brains have an excellent filtering mechanism that helps switch our attention rapidly from one thought to the next.

At the same time, rather than lose unattended thoughts, the mechanism keeps them active in the recesses of the brain.

The more we juggle, however, the less efficient we become at performing any one task. And the longer we go before returning to an interrupted task, the harder it is to remember just where we left off.

Not surprisingly, laboratory research shows that multitasking increases stress, diminishes perceived control, and may cause physical discomfort such as stomach aches or headaches. Our own research on more than 25,000 people worldwide demonstrates that Multitasking Madness makes it ever harder to concentrate for extended periods. You might notice that as you are working on one task, thoughts about another creep into your consciousness. This is that filtering mechanism, doing its work keeping important tasks close at mind. Another sign of Multitasking Madness is the feeling that your memory is not quite as good as it used to be. You start working on something and then find yourself not being able to remember what you wanted to do or say. Still another symptom is an inability to sustain a peaceful night's sleep or to enjoy what used to be calming, recreational times. Too many thoughts are buzzing in your head.

In the end, Multitasking Madness diminishes your productivity and makes you work harder just to feel like you are barely keeping up with all your work.

Yet if you look around you you'll see people multitasking everywhere, largely because of technology. People even check pagers and answer cellular phones on the golf course. Research shows that our eroding ability to estimate time accurately also contributes to Multitasking Madness. Ask someone how long it will take to download, read, and answer e-mail. Then check the actual time. You'll generally find that the person underestimated the time required. This discrepancy leads us to pile more expectations on ourselves. We multitask more and more, and soon we have way too much to juggle.

But you can stop the Madness.

First and foremost, you must become better at estimating the time it takes you to complete a task. Make a list of all the tasks that you plan to complete during, say, a four-hour period and then write down how long you think that each task will take. Now, time yourself. You'll find the percentage by which you typically underestimate, and you can adjust your expectations. Of course, you also have to learn to say no to tasks you don't have time to complete.

Second, you should develop an external memory to take some of the load off your brain. An external memory can be as simple as a pad of paper. Once you list the tasks you're juggling, your mind feels comfortable letting go of the memory traces, and your filter gets a chance to rest. This sort of multitasking break is particularly effective right before you go to sleep. If you find yourself awakening in the middle of the night, dump your thoughts on a pad of paper that you keep by the side of the bed. Sleep should come back soon.

Third, you need to give yourself a chance to persevere on a task until completion—the most productive way to work. This may require removing distractions: turning off most programs on your computer, not checking your e-mail, and turning off the ringer on your phone and fax.

Fourth, you need "down time"—watching a baseball game, playing with your children, going to a movie with your spouse. This is crucial to refresh your system and let you return to your work with a clean perspective and the ability to work more effectively.

Remember, technology can multitask forever. You cannot.