Higher plate counts on MRS agar were obtained under anaerobic conditions for three of four strains of Lactobacillus acidophilus and commercially prepared nonfermented acidophilus milks (products A and B) made with two of the strains. Average values for aerobic counts of products A and B were 87 and 60%, respectively, of those for corresponding anaerobic counts. Incubation of plates poured with MRS agar for 72 ± 3 h at 37 C was sufficient for maximal counts. Two strains and the nonfermented acidophilus milks gave highest counts on Standard Methods Agar (SMA). Greatest numbers of bile-resistant colonies were indicated by MRS agar (with 0.2% oxgall). The average of plate counts for products A and B determined on MRS agar with oxgall was 65% of that for corresponding plate counts determined on MRS without oxgall. Buffered distilled water, 0.9% NaCl, and 1% peptone each served satisfactorily as diluent. Overlaying MRS agar in poured plates with additional medium was not advantageous. Plate counts of samples that had been frozen and stored at −26 C or in dry ice were as high as those of duplicate samples that had been stored at 1.7 C.