It has been suggested that there is a difference in the interaction between sex steroids and gonadotropin secretion between transsexual and heterosexual women. In this study we tested whether there is a difference in the pulsatile release characteristics of luteinizing hormone (LH) and in ovarian steroid concentrations between 16 female-to-male (f-to-m) transsexuals and eight eugonadal heterosexual women during the early follicular phase of the menstrual cycle. Blood samples for LH determination were collected every 10 min for 7 hr in the transsexual group, and every 10 min for 6 hr in the heterosexual group. There were no significant differences between the transsexual and heterosexual group in mean serum LH concentration (6.9±2.4 U/l vs. 7.5±2.6 U/l), mean LH nadir interval (77±37 min vs. 70±16 min), and mean LH pulse amplitude (2.9±1.1 U/l vs. 3.0±1.1 U/l). Serum estrone, 17-β-estradiol, testosterone, progesterone and FSH concentrations also did not differ between the two groups. There also was not a higher prevalence of polycystic ovarian disease in our f-to-m transsexual group than in the general population.