Epidermal growth factor (EGF), a polypeptide hormone originally discovered in the mouse submaxillary gland, stimulates growth in a variety of tissues in several species. This hormone has recently been identified in human urine. A homologous RIA for human EGF (RIA-hEGF) has been developed. In general, levels were similar to those recently reported using a heterologous RIA system. Twenty-four-hour urinary excretion of RIA-hEGF by normal adult males and females was 63.0 +/- 3.0 and 52.0 +/- 3.5 (mean +/- SE) micrograms/total vol, or 29.7 +/- 1.1 and 39.8 +/- 1.7 micrograms/g creatinine, respectively. Excretion by females taking oral contraceptives was significantly greater (60.1 +/- 2.7 micrograms/g creatinine; P less than 0.01) than that by females who were not. Recent evidence suggests the probable identity of hEGF and beta-urogastrone, a potent inhibitor of gastric acid secretion. Adult males with active peptic ulcer disease appeared to have lower urinary RIA-hEGF excretion (22.9 +/- 2.6 micrograms/g creatinine) than normal men, but this was not significant (P greater than 0.05). Several of those with very low values had histories of alcohol abuse. Excretion by patients with Cushing's syndrome was normal. Patients with psoriasis or recovering from major burns excreted both abnormally high and abnormally low levels of RIA-hEGF, with no obvious correlation to their clinical condition. There was no apparent diurnal or postprandial variation in urinary RIA-hEGF excretion by normal subjects. An excellent linear correlation was observed between RIA-hEGF and creatinine concentrations in each urine sample for each subject, suggesting that RIA-hEGF concentration in a random urine sample provides a valid index of 24-h RIA-hEGF excretion.