Four normal male subjects received LHRH by continuous infusion for 72 hrs at 1.4 microgram/min. Mean basal LH was 7.7 +/- 1.0 mIU/ml, increased to a maximum of 120 +/- 22.7 mIU/ml, and then declined to levels between 28--34 mIU/ml for the last 30 hrs of infusion; FSH rose from 3.7 to 11.4 mIU/ml (p less than 0.05) at 16 hrs and then returned to baseline. Testosterone levels rose by 50% at 12 hrs, and remained elevated throughout with maximum values between 6.6 and 12 ng/ml. Estradiol-17beta levels were 26.2 +/- 4.7 pg/ml basally, rose to 104 +/- 8 pg/ml and while levels declined therafter, they were significantly above baseline throughout the 72 hrs. Plasma androstenedione and dehydroepiandrosterone levels also showed significant increases. By contrast, transient elevations in pregnenolone and 17-hydroxypregnenolone levels probably corresponded to the nomral morning rise in plasma levels of these steroids; 17-hydroxyprogesterone rose from 1.3 +/- 0.15 to 3.9 +/- 0.26 ng/ml at 12 hrs and remained elevated through the infusion. An increase in 17-hydroxyprogesterone:testosterone ratio was observed in all subjects. Thus, chronic LHRH infusion effected a persistent increase in endogenous LH with, in turn, prolonged stimulation of gonadal steroid secretion.