Urinary gonadotropin concentrations were determined by polyclonal double antibody RIA after ammonium sulfate extraction. Good correlation was observed between urinary gonadotropin/creatinine ratios in first morning voided and full 24-h urine collections. Using consecutive 30-d first morning voided urine specimens from normal children and from patients with sexual disorders, we have studied the monthly patterns of nighttime gonad-otropin secretion. In normal prepubertal girls, the levels of urinary LH were low with few variations and those of urinary FSH were higher with episodic fluctuations. In early puberal girls, the levels of urinary LH increased with striking, rhythmic fluctuations. The same changes were seen in urinary FSH. A single big surge of urinary gonadotropins was observed in postmenarcheal girls, In normal boys, the secretory patterns of urinary gonadotropins were similar to those of normal girls, but varied less. In patients with idiopathic precocious puberty, the patterns of urinary gonadotropins were similar to those of normal subjects matched for sexual stage. The measurement of 30-d first morning voided urinary gonadotropins can provide a simple and physiologic test of gonadotropin function in children. (Pediatr Res 28: 405–410,1990)