Epidermal growth factor (EGF)/urogstrone is a polypeptide hormone that stimulates growth of a variety of tissues and inhibits gastric acid secretion. Although it was originally isolated from male mouse submaxillary glands, EGF/urogastrone has recently been isolated from human urine. We detected EGF-like activity in human urine, milk and saliva by radioreceptor assay using the male mouse hepatic microsomal fraction as a receptor preparation and mouse EGF as reference standard. On Sephadex G-50 gel chromatography, major EGF-like activity (RRA-EGF) in human urine, milk and saliva was eluted near the portion where standard mouse EGF was eluted (Kav = 0.5, MW approximately equal to 6000). Isoelectric focusing revealed that isoelectric point of major RRA-EGF was 4.45 with minor heterogeneity. Twenty-four hour urinary excretion of RRA-EGF in adult males and females with normal renal function was 88.8 +/- 4.0 and 65.2 +/- 7.9 (mean +/- SE) microgram/total volume or 141 +/- 7.2 and 96.5 ng/mg of creatinine, respectively. There was no apparent diurnal rhythm in urinary RRA-EGF excretion. A series of 24 h urine collection over 5 days from adults showed relatively small variations. Urinary levels of EGF per mg creatinine in normal children were significantly higher than those in normal males or females. There was a reverse correlation between serum creatinine levels and urinary EGF levels per creatinine. The concentration of RRA-EGF in human milk collected 7 days after starting breast feeding was 81 +/- 11 ng/ml. The salivary RRA-EGF concentration was 6.5 +/- 1.0 and 6.9 +/- 0.3 in normal adult males and females, respectively.