One-centimeter cubes of the semimembranosus and adductor muscles of beef were inoculated with 5.2 × 106 of Salmonella typhimurium, Shigella sonnei, Yersinia enterocolitica, Escherichia coli, Pseudomonas aeruginosa or Streptococcus faecalis. Exposure of the meat by dipping in 1.2% acetic acid for 10 s reduced averge numbers recoverable of these bacteria by 65%. E. coli was the most resistant, losing 46% of its viable cells. One-half of the acetic acid was replaced with 0.046% formic acid without loss in effectiveness. The rate of increase in antimicrobial effects of the treatment declined with time. Discoloration of the meat occurred after dipping in both 1.2% acetic acid, and 0.6% acetic plus 0.046% formic acids for 10 s. In triangle tests of flavor, panelists failed to differentiate samples of baked ground beef treated (before grinding) with 0.6% acetic acid and 0.046% formic acid from controls dipped in water (P<0.05). However, the same type of test showed a significant flavor difference between meat dipped in 1.2% acetic acid or distilled water.