This study tested whether there is a difference in the pulsatile LH secretion between male-to-female transsexuals and eugonadal heterosexual men. The mean serum LH concentrations, the LH pulse frequency, and the LH pulse amplitude were compared between a group of eight male-to-female transsexuals and a group of 22 heterosexual men. Blood samples for LH determinations were collected every 10 min for seven hours. 17-β-estradiol and testosterone were measured at the beginning of each test. There were no significant differences between the heterosexual and transsexual group in LH pulse frequency (3.9±1.3 vs. 3.9±1.7), LH pulse amplitude (3.7±1.3 U/l vs. 3.0±0.5 U/l), mean serum LH concentration (5.2±1.4 U/l vs. 5.4±1.1 U/l), 17-β-estradiol (0.07±0.01 nmol/l vs. 0.08±0.02 nmol/l), or testosterone (22.9±3.7 nmol/l vs. 21.8±8.0 nmol/l). We conclude that the pulsatile release characteristics of LH do not allow a distinction between eugonadal heterosexual men and eugonadal male-to-female transsexuals.