A simple and improved method for the quantification of urinary LH and FSH was developed. Urinary gonadotropin concentrations were determined by polyclonal double antibody RIA after ammonium sulfate extraction. Urinary LH and FSH concentrated by ammonium sulfate were coeluted with an iodinated LH and FSH tracer. Gel chromatography of the urine revealed that the majority of immunoreactive LH and FSH were eluted coincident with125I-LH and125I-FSH. Good correlation was observed between urinary gonadotropin/creatinine ratios in first morning voided and full 24-h urine collections. Age-de-pendent changes in urinary LH excretion were significant in normal boys and girls 6–17 y of age. Urinary FSH excretion in these children did not change in an age-dependent fashion. (Pediatr Res 28: 401–404,1990)