We evaluated the extent and effects of bacterial contamination of an open continuous enteral feeding system. Eighty-two quantitative enteral feeding cultures and clinical data were obtained during 8 days of observation on each of 33 patients. Cultures of appropriate sites were obtained on febrile patients and compared to the enteral feeding culture. Gram negative bacilli (GNB) in the enteral feeding correlated with abdominal distension in the patients (10 of 12 patients with GNB compared to 5 of 21 without GNB; p less than 0.01). Nine of the 10 patients with GNB and distension were receiving systemic antimicrobics to which the organism was resistant. Contamination of feeding with Serratia marcescens correlated with cultures for the same organism in patients' other body sites (p less than 0.01). The feeding contaminant may have been the source of sepsis in one patient who expired from septic shock. No relationship was demonstrated between contamination and liquid stools or fever. Undiluted, canned feedings were significantly less contaminated at 24 hr (15%) than those requiring mixing of powder (94%) (p less than 0.0001). The canned feedings grew primarily enteric organisms, whereas the powder feedings grew flora typically resident on the skin. Mixing or diluting feedings appears to represent an increased risk of contamination. Growth of GNB may produce adverse effects. Further investigation into methods to limit contamination and growth is warranted.