Summary:The incidence of the main types of bacteria among 2,856 isolated on Yeastrel‐milk agar incubated at 30° from 121 rinses of dairy equipment cleansed by chemical methods, showed that micrococci were dominant in low colony count (<104/ft2) rinses of equipment treated by immersion cleaning in caustic soda or cleansed in detergent‐hypochlorite solutions, whereas nonpigmented Gram‐negative rods were dominant in low count rinses of equipment cleansed with detergent‐sterilizers containing quaternary ammonium compounds. Gram‐negative rods were dominant and streptococci frequent in high count (<2·5 × 105/ft2) rinses irrespective of the chemical used. A high proportion of the streptococci and coli‐aerogenes organisms gave acid reactions in litmus milk after 72 h at 22°, many of the anaerogenic Gram‐negative rods and several of the aerobic sporeformers gave proteolytic reactions, whereas the majority of the micrococci, corynebacteria and other asporogenous Gram‐positive rods showed no change. Bacteria isolated from high count rinses were more active in producing milk spoilage reactions at 22° than those isolated f