SuMlMARY: A liquid medium buffered at pH 9.6 is described which is modified from that of Shattock & Hirsch (1947) by the addition of phenolphthalein and in the method of preparation. Its use in distinguishing streptococcal species was investigated. Shattock & Hirsch (1947) described a liquid glycine-buffered medium for testing the ability of streptococci to grow at pH 9.6, one of the criteria found useful by Sherman & Stark (1934) and Shattock & Mattick (1943-44) for distinguishing Streptococcm faecalis from Strep. ladis. This medium was used by Shattock (1949) and by Sharpe & Shattock (1952) in studies on group D streptococci and Strep. Zactis. It was thought that if a suitable indicator could be added to the medium it might be possible to dispense with the electrometric measurement of pH value, and as streptococci readily produce acid from glucose, growth would be accompanied by a change in colour of the indicator. Phenolphthalein with a pK of 9-7 was selected. PREPARATION OF MEDIUM