Basal and TRH stimulated plasma prolactin levels were determined in 24 pubertal boys with hypogonadism (Primary: n = 10; secondary: n = 4; tertiary (hypothalamic): n = 10) and controls matched for pubertal stage (n = 12). The differentiation between secondary and tertiary hypogonadism was made with the help of a prolonged LRH test. The TRH test was performed by injecting 200 mcg i.v. in one bolus and taking plasma samples at 0, 15, 30, 60 and 90 minutes. No statistically significant differences were found between any of the groups. It is concluded that determination of basal or TRH stimulated prolactin does not contribute to clarify the etiology of hypogonadism or to determine the grade of damage or dysfunction in the hypogonadic testes.