Clinicians often find that the application of pharmacokinetic principles for the calculation of a drug regimen is bewildering and difficult. In this article it is shown that clinically useful calculations can be simply done at the bedside using a handheld calculator. The only requirement is an understanding of the terms that define the pharmacokinetic behavior of a drug. Appropriate manipulation of these terms will allow calculation of loading and maintenance doses, peak and average plasma concentrations, and other useful pharmacological data. The result will be improvement in drug therapy.