A medium devised primarily for lactic streptococci and their phages but also recommended forLactobacillus bulgaricuswas found to be inhibitory to many strains ofL. bulgaricus. The inhibition was attributed to the buffering agent, β‐glycerophosphate, in the medium and could also be demonstrated when this buffer was incorporated in other media. Since the glycerophosphate containing medium supported good growth ofStreptococcus thermophilusit was applied successfully to selectively isolate this organism from yoghu