The pharmacokinetics of nandrolone in serum and urine were investigated in healthy young men after a single im injection of 50 mg (n = 20), 100 mg (n = 17), or 150 mg (n = 17) nandrolone decanoate. Blood samples were collected before treatment and for up to 32 d after dosing. In addition, in the 50- and 150-mg groups, 24-h urine samples were collected before treatment and on d 1, 7, and 33 after treatment; in the 150-mg group, additional samples were collected after 3 and 6 months. Serum concentrations and the area under the curve of nandrolone increased proportionally with the dose administered. The peak serum concentration ranged from 2.14 ng/ml in the 50-mg group to 4.26 ng/ml in the 100-mg group and 5.16 ng/ml in the 150-mg group. The peak serum concentration was reached after 30 h (50 and 100 mg) and 72 h (150 mg), whereas the terminal half-life was 7-12 d. In urine, pretreatment concentrations of 19-norandrosterone (19-NA) and/or 19-noretiocholanolone (19-NE) were detected in five of 37 subjects (14%). In the 50-mg group, 19-NA and/or 19-NE could be detected at least until 33 d after injection in 16 of 17 subjects (94%). In the 150-mg group, who were presumed to have not previously used nandrolone, nandrolone metabolites could be detected for up to 6 months in eight of 12 subjects (67%) for 19-NE and in 10 of 12 subjects (83%) for 19-NA.