The study of the pharmacokinetic (PK) behavior of a compound is crucial to understand the absorbtion, distribution, metabolism and elimination of a drug by the body. PK studies involve measuring the concentration of the drug in the plasma or blood at several time points post drug administration. The classic complete data design samples each subject at all predefined time points. Ethical considerations and restrictions in blood volume, however, lead to incomplete data designs being frequently used instead. In serial sampling designs only one sample is taken from each subject, whereas batch designs take samples more than once from each subject, but not at all time points. In this manuscript the R package PK, which enables the computation of various PK parameters in complete and incomplete data designs, is introduced and some examples are given. Copyright © 2010 John Wiley & Sons, Ltd.