Six episodes of gram-negative bacteremia and seven pyrogenic reactions occurred in 11 patients in one hemodialysis center. Gram-negative bacter-emias and/or pyrogenic reactions were not related to reuse and were more likely to occur if dialysis was performed in one unit of the center (8/13 unit 5 vs. 221/1,151 in other units, p < 0.001) and with one type of dialysis machine (10/13 vs. 581/1,151 with other machines, p = 0.05), which was preferentially used in unit 5 (p < O.Ol). Bacterial and endotoxin concentrations of water used to prepare dialysate and reprocess hemodialyzers, and of dialysate, exceeded allowable concentrations recommended by the Association for the Advancement of Medical Instrumentation (AAMI). The implicated dialysis machines were disinfected with chemicals daily, but not heat-disinfected daily as suggested by the manufacturer. Results suggest that the outbreak was caused by the use of water that did not meet AAMI standards and inadequate disinfection of one type of dialysis machine.