The pharmacokinetics of Chlormezanone (CM) has been determined after a single oral dose of 400 mg CM in 5 young volunteers (28 y) and in 8 elderly patients (79 y). In the young subjects, CM was rapidly absorbed and distributed, and was slowly eliminated with a half-life of 38 h major metabolites were not detected in plasma or urine. Only 3% of CM was excreted unchanged in urine. In elderly patients absorption was delayed but not reduced; the Cmax and AUC did not differ from those in younger subjects, the elimination rate was reduced compared to the younger subjects (mean 54 h). The increase was in part related to the reduction in renal function and metabolism observed in aging. However, the change in pharmacokinetics was moderate and no adjustment in dosage seems necessary for treatments of limited duration in elderly patients.