Mean protein intake in a 4-day dietary survey of 34 patients with early renal disease was 1.2 +/- 0.27 g/kg ideal body weight daily. Nine subjects were taking over twice the recommended minimum intake. An increased protein intake was associated with a greater phosphate and sodium intake and an increased excretion of urea, phosphate, and sodium. Daily intake fluctuated markedly during the study (coefficient of variance 22.5 +/- 10.9%). Protein catabolic rate calculated from urea excretion correlated with protein intake, r = 0.60. Mean difference between the two estimates was 0.04 +/- 0.28 g/kg per day. It is proposed that if urea excretion exceeds 4.5 mmol/kg per day in a single collection (protein catabolic rate 0.98 g/kg per day), serial measurements should be made to determine protein intake more accurately and give dietary advice.