To investigate the relationship between gonadotrophins, androgens and testicular descent in the pig fetus, serum concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and serum concentrations and testicular content of testosterone (T) and 5 alpha-dihydrotestosterone (DHT) were determined by radioimmunoassay in 95 fetuses (48 males, 47 females) between Day 60 and Day 90 post coitum (p.c.). The testes were descended in 0% of fetuses at Day 60, 8% of fetuses at Day 70, 40% of fetuses at Day 80 and 87% of fetuses at Day 90 p.c. There was a significant increase in mean serum concentrations of LH in both male and female fetuses from Day 60 to Day 90, with a significant difference in mean serum concentrations of LH between male fetuses with a body mass < 350 g (4% of testes descended) and those with a body mass > 450 g (87% of testes descended), but not between male and female fetuses < 350 g or > 450 g in body mass. There was no significant difference in mean serum concentrations of FSH between male and female fetuses. Mean serum concentrations of T were significantly higher in male fetuses at Day 60 than in those at Days 70-90, with no significant difference in serum concentrations of DHT from Day 60 to Day 90 p.c. Testicular content of T and DHT showed a non-linear increase from Day 60 to Day 90 p.c. Although the serum concentration of T is elevated before, and decreased during, the period of descent, the testicular content of T and DHT increases during the period of descent, indicating that serum concentrations of LH and FSH may have an indirect effect on descent by stimulating testicular androgen synthesis.