[Development of blood testosterone levels in the fetal rabbit during sexual organogenesis]

Testosterone was measured daily by radio-immunoassay from the 18th to the 25th day of gestation in 650 male and female fetuses. In male fetuses testosterone levels increased between days 18 and 19, reaching their maxima at 20 days and varied little from 21 to 25 days. Circulating concentrations of testosterone were sex-dependent.