The rapid clinical evaluation of new drugs active against human immunodeficiency virus (HIV) requires that pharmacologic properties be carefully considered to determine optimal exposure profiles in patients. The published pharmacokinetic data for the nucleoside antiretroviral agents zidovudine, didanosine, zalcitabine, stavudine, and lamivudine show that administration offixed doses ofcertain agents results in a considerable degree ofbetween-patient variability in in vivo drug exposure. Pharmacologic treatment of HIV infection requires development of strategies for individualized adjustment of doses of certain agents with a high degree of interpatient variability.