Septicemia caused by contaminated infusion fluid is a newly appreciated hazard of intravenous infusion therapy. Microorganisms of the tribe Klebsielleae (Klebsiella, Enterobacter, and Serratia) have predominated in these infections. Members of this tribe found to possess a selecive ability over common non-Klebsielleae microbial pathogens to proliferate rapidly in commerical parential fluids contaning clucose at room temperautre. Fifty-one Klebsielleae strains, washed twice before inoculation of approximately 1 organism/ml, attained a mean normalized 24 hr concentration of 1.11 x 10-5 organisms/ml in 5% dextrose in water at 25 C. In contrast, 48 of 49 non-Klebsielleae bacterial strains (clinical isolates of Staphylococcus, Proteus, Escherichia coli, Herelea, and Pseudomonas aeruginosa) slowly died (mean 24-hr concentration, 0.2 organism/ml). Five Candida albicans strains frew only very slowly (31.3 organisms/ml). Even with concentrations exceeding 10-6 organisms/ml, microbial presence was never visibly detectable. The significant increases in cases of nosocomial spticmia caused by Klebsiella, Enterobacter, and Serratia in recent years might be attribuatble in part to fluid-related spesis accompanying the expanding use of parenteral therapy.