In chronic renal failure, epidermal growth factor (EGF) excretion is decreased. In this study, asymptomatic adult polycystic kidney disease (APKD) patients with a relatively preserved glomerular filtration rate were examined. Excretion of EGF was studied in 6 patients with APKD (median age 42 years; serum creatinine [median] 95 [range-80-133] mumol/l) and compared with that of 28 healthy controls. EGF was determined in a spot morning urine by using a specific radioimmunoassay, and expressed in relation to creatinine excretion. Excretion of EGF in APKD was (median) 157 (range-13-359) and in the controls (median) 546 (range-238-1199) pmol/mmol creatinine (p < 0.001). Low excretion of EGF in APKD patients with preserved kidney function suggests a distal abnormality at an early stage of the disease, prior to the development of renal failure.