The authors observed a wide variability in the number of uses per dialyzer in their hemodialysis patients. In 54 patients who reused their dialyzers, heparin dose (U/kg/min) related directly and white blood cell count related inversely to reuseability. Average reuse was 5.1 ± 2.9 (SD) in diabetics (n = 13) and 7.8 ± 3.8 (SD) in non-diabetics (n = 41;p = 0.007). Of the diabetics, 77% achieved six or less reuses, and 59% of non-diabetics achieved six or more reuses (chisquare = 4.96; p < 0.05). In non-diabetics, heparin dose was the most significant determinant of reuse, and in diabetics, the major determinant was white blood cell count. Hematocrit levels, platelet count, erythropoietin use, or type of membrane (polysulfone/cellulose acetate) did not correlate with reuseability. It was concluded that reuseability of dialyzers is less in diabetic patients, patients on lower heparin doses (U/kg/min), and patients with higher white blood cell counts. Determinants of dialyzer reuseability warrant further study.