Brochothrix thermosphacta, Enterobacteriaceae and the Pseudomonas-Moraxella group grew more rapidly on the fat than on the lean surfaces of chilled vacuum-packaged beef striploins of pH 5.45–5.85. On the fat, both B. thermosphacta and Enterobacteriaceae grew to outnumber the Pseudomonas-Moraxella. When Enterobacteriaceae and B. thermosphacta were present initially in about equal numbers, Enterobacteriaceae outgrew B. thermosphacta on both the fat and the lean surfaces of packs stored at 5°C. At 1°C the growth rate of the Enterobacteriaceae was greatly reduced. As a result, on the fat at 1°C, B. thermosphacta grew considerably faster than did the Enterobacteriaceae.