Androgen metabolism by human epiphyseal cartilage and chondrocytes in primary culture was studied during fetal life. Testosterone (T) and androstendione (Δ4) were incubated with epiphyseal cartilage and with chondrocytes in Dulbecco's medium for 4, 12, and 24 h. Androstanedione, Δ4, dihydrotestosterone (DHT), and androstanediol were separated by bidimensional thin layer chromatography and Δ4, DHT, and T recrystallized in five different solvent systems. The results showed that Δ4 was transformed into androstanedione, DHT, and T whereas T was metabolized into Δ4 and 5α-reduced androgens. In both systems (epiphyseal cartilage and chondrocytes) Δ4 was the principal metabolite produced from T. There were no major differences in the metabolic patterns of Δ4 and T between epiphyseal cartilage and chondrocytes according to sex nor gestational age (11–32 weeks). In conclusion, 5α-reductase activity was found in chondrocytes from human fetuses of both sexes, but T was mainly transformed into Δ4. © 1984 by The Endocrine Society.