OBJECTIVE To quantify glucose balance related to continuous arteriovenous hemofiltration (CAVH) when a glucose-rich replacement fluid is used for the plasma ultrafiltrate removed. METHODS Prospective, nonintervention study. METHODS Medical/surgical and cardiac surgical intensive care units of a university hospital. METHODS Critically ill patients (n = 20) with acute oliguric renal failure undergoing CAVH. METHODS None. RESULTS Timed collections of CAVH effluent were analyzed and other observations were made. Serum creatinine and blood urea nitrogen concentrations decreased substantially during CAVH in each patient. The mean measured glucose concentration of the replacement fluid (Dianeal 1.5%) was 1.40 +/- 0.11 (SD) g/dL (77 +/- 6 mmol/L) and rate of infusion was 1.39 +/- 0.43 L/hr. Effluent volume was 1.51 +/- 0.49 L/hr and glucose was 0.47 +/- 0.10 g/dL (26 +/- 5 mmol/L). The glucose content of the replacement fluid infused was consistently and substantially greater than that value of the effluent removed during the same period. Thus, the average net glucose uptake in relation to the CAVH circuit was 11.9 +/- 3.1 g/hr (range 4.3 to 17.6). Serum glucose concentrations increased in each patient with initiation of CAVH (from 135 +/- 44 to 278 +/- 80 mg/dL [7.4 +/- 2.4 to 15.3 +/- 4.4 mmol/L]; p < .001). Negative fluid balance achieved during CAVH was approximately 100 mL/hr. CONCLUSIONS CAVH using predilution with replacement fluid is effective in managing uremia and fluid overload in critically ill patients. The use of a glucose-rich replacement fluid is accompanied by the net uptake of large amounts of glucose, approaching 300 g/day on average in our patients and representing a major exogenous calorie source. This finding has important implications for the metabolic management of critically ill patients during CAVH and should be taken into account in prescribing their nutritional support.