To determine the relationship of gonadotropin excretion to spermarche, 26 boys ranging in age from 10.3 to 17.5 years each provided ten overnight urine samples. Microscopic observation of sperm was found in 33 (13%) of the 260 samples, with 50% of the boys exhibiting sperm in at least one specimen. No further cumulative gain in detecting spermaturia occurred after the seventh urine collection. The median age of spermarche was computed by logistic regression analysis to be 14 years. Three urine collections from each boy were assessed for gonadotropin levels. At age 14 years mean follicule-stimulating hormone and luteinizing hormone excretion were, respectively, 857 and 503 mIU/h, into the reported adult daytime range. Spermarche is a midpubertal event associated with age-appropriate gonadotropin production.