The plasma pharmacokinetics and urinary excretion of thalidomide have been evaluated in eight healthy male volunteers receiving a single oral dose of 200 mg. Concentrations of thalidomide were determined by a new HPLC assay. Plasma concentration vs. time data were well fit by a one-compartment model. The mean (+/- SD) peak concentration, 1.15 +/- 0.2 microgram/ml, was achieved at 4.39 +/- 1.27 hr. Absorption and elimination half-lives were 1.70 +/- 1.05 hr and 8.70 +/- 4.11 hr, respectively, with a lag time of 0.41 +/- 0.17 hr observed in six subjects. The apparent volume of distribution and total body clearance rate, based on assumed complete bioavailability, were 120.69 +/- 45.36 liters and 10.41 +/- 2.04 liters/hr. The urinary excretion of thalidomide accounted for only 0.6 +/- 0.22% of the total dose administered over 24 hr, and the renal clearance rate was 0.08 +/- 0.03 liter/hr. This suggests that the major route of elimination of thalidomide is nonrenal.