Examination of a holder pasteurizing plant giving occasional apparently inexplicable phosphatase test failures proved that excessive froth on the surface of the milk during holding, resulting from an unsuitable type of pre‐heater, was causing the trouble. Uninsulated lids allowed considerable loss of heat from the froth. Other plants of the same make were examined and the same inherent faults found.Two other makes of holder plant with well insulated lids were also tested. There was a large air space under the lid in one plant in which phosphatase test failures occurred in the froth and surface milk, whereas the other plant, with no air space, gave no failures.One hundred bacterial cultures from two bulked froth samples from two plants were tested for heat resistance. A number of these, including a streptococcus, a sarcina, a micrococcus, and several Gram‐negative rods, were found to have heat resistance similar to that of tubercle baci