Bacteriophage active against a lactic streptococcus was first isolated in this laboratory in February 1935. In May of the same year some batches of phage for Streptococcus cremoris strain HP were prepared by lysing the bacteria in skim-milk culture and preparing a Seitz-filtered whey as described by Whitehead & Cox(1). At that time it was not the practice to adjust the reaction of phage filtrates and the pH of the batches prepared in 1935 was not recorded. It was probably between 5·2 and 6·1 (Hunter & Whitehead (2)). Samples of four different preparations of the phage were filled into sterile tubes and sealed off in a blow-pipe flame. Two of the samples, sealed on 24 May 1935, had titres of 107 (as determined by spotting of standard loops of dilutions on a bacterial mat) and the other two, sealed on 16 July 1935 had titres of 106. The sealed tubes were stored in the refrigerator at 4–7° C.