F. RUÍZ‐TERÁN AND J.D. OWENS. 1996. The effect of pH on the heat resistance ofBacillus stearothermophilusspores at 100°C in the presence of 0.11 mol 1‐1lactic acid and 0.2 mol 1‐1sodium phosphate buffer was examined. At pH values of 7.0 and 6.0 spores survived 60 min exposure unharmed but at pH 4.3 and 3.0 they died with decimal reduction times (DRTs) of 27 min and 2.8 min, respectively. Death rates were similar in the presence or absence of hydrated soybean cotyledons. In the presence of phosphate buffer and cotyledons at mean pH 3.6 the DRT was 118 min but in the presence, in addition, of lactic acid it was 11 min. It is suggested that the enhanced death rate was due to toxic effects of undissociated lactic acid.Rhizopus oligosporusNRRL 2710 grew well on cotyledons, having pH values from 7.0 to 3.7, prepared by boiling for 60 min in the presence of 0.11 mol 1‐1lactic acid and 0.2 mol 1‐1phos