Microbial growth in enteral nutrition solutions (ENS) has frequently been documented. To determine the relation of this contamination to nosocomial infection, we prospectively studied 24 intensive care unit patients who received enteral feeding. Cultures of solutions were obtained while refrigerated and during administration as well as pharyngeal and rectal cultures from patients at the start of enteral nutrition and serially during administration. Most patients (10/16, 62.5%) receiving solutions mixed on the ward and 3/14 (21.4%) receiving solutions prepared elsewhere appeared to become colonized (0.05 less than P less than 0.10) by organisms initially isolated from feeds. By antibiotic susceptibility and plasmid analysis, eight patients were found to be colonized by 11 organisms identical to those which were first isolated from ENS. Two of these patients had ENS-associated pneumonias caused by Acinetobacter baumannii. Solutions often contained multiple Gram-negative bacilli similar to those recovered from nurses' hands and blenders, in numbers up to 1 x 10(8) ml-1. We conclude that ENS may be an important source of nosocomial infection. Uniform microbial criteria for ENS should be developed and methods to limit contamination should be utilized.