The pharmacokinetics of tetrazepam (Myolastan, Musaril), were studied in 12 healthy volunteers. Tetrazepam was given orally as a single dose of 50 mg and repeated administration for 5 consecutive days of 50 mg at 12-h intervals, in tablet form. Tetrazepam was measured in plasma using a selective and sensitive GLC method. Tetrazepam is rapidly absorbed after oral administration with a peak plasma level of 0.49 +/- 0.10 mg/l at 0.94 +/- 0.47 h. The drug is widely distributed in the organism with an apparent volume of distribution of 6.7 +/- 2.1 l/kg. Tetrazepam is eliminated with a half-life of 22 +/- 4 h and can be classified as a benzodiazepine with medium half-life value. This medium half-life is the result of the high hepatic clearance of the drug in spite of its large distribution volume. Since in this study 6 male and 6 female volunteers were studied it was possible to compare the pharmacokinetic profile in the two groups. No significant differences were observed. No differences were observed between the pharmacokinetic values after a single dose or after repeated administration.