SUMMARYA comparison has been made of the disinfecting efficiency on cows' teats of a hypochlorite and a quaternary ammonium disinfectant. Little difference in efficiency was found between the disinfectants when used at 200 p/m. Hypochlorite was slightly more effective in eliminating coli‐aerogenes bacteria, but there was no evidence of greater survival of other Gram‐negative organisms with the quaternary disinfectant. Micrococci were the main survivors and, in summer, coagulase positive staphylococci formed a considerable proportion of th