OBJECTIVE We compared the relationship of protein intake (as measured by protein nitrogen appearance) and dialysis delivery in insulin-dependent diabetic (IDDM) and nondiabetic patients. METHODS One to two 24-hour dialysate and urine collections were obtained in 20 diabetic patients and 42 nondiabetic patients. The protein equivalent of nitrogen appearance (PNA) was calculated by the Randerson formula. KT/V was determined using V obtained by the Watson formula. PNA was normalized using three different methods to determine body weight: first, by normal or ideal body weight according to the Metropolitan Table (nPNA); second, by standard body weight according to the NHANES Table (sPNA); and third, by V/0.58 (vPNA). RESULTS The mean PNA was not different in diabetics and nondiabetics (53 +/- 21 g/day vs 60 +/- 14 g/day), nor was weekly KT/V (2.1 +/- 0.6 vs 2.1 +/- 0.6). Mean normalized PNA was not different in IDDM versus non-DM regardless of the method. KT/V correlated with nPNA in IDDM (r = 0.54, p = 0.002 and non-DM, r = 0.31, p = 0.03), and with vPNA in IDDM (r = 0.73, p < 0.00001, and non-DM, r = 0.45, p = 0.0009). KT/V also correlated with sPNA in IDDM (r = 0.57, p = 0.001), but not in non-DM (r = 0.25, p = 0.08). The slope for normalized PNA versus KT/V was steeper for IDDM than for non-DM. CONCLUSIONS KT/V and PNA are more closely correlated in IDDM patients than in non-DM patients. Thus it is extremely important that IDDM patients receive an adequate level of dialysis.