The importance of bacteriophage in dairy fermentations has resulted in extensive research during the past two decades. This work has been reviewed by Elliker (1951). Recently a more fundamental approach has been used, and methods developed in other areas have been applied to the study of lactic streptococcus bacteriophage. Employing the one-step growth technic of Delbruck and Luria (1942), Cherry and Watson (1949) reported on the growth characteristics of a strain of lactic streptococcus bacteriophage. They observed in tryptone yeast extract broth following 10 minutes' adsorption a latent period of virus growth in the range of 31 to 33 minutes, a rise period of 15 to 18 minutes and an average burst size of 70 plaque-forming particles per infected cell. As their investigation was made with but one strain of the virus in only one medium, it seemed desirable to extend the study. In the present work experiments were conducted with three bacteriophage strains, each studied in two media differing in level of definition. To determine the extent of variation in sizes of individual bursts, and for comparison with average burst size evaluated from one-step growth curves, burst size also was studied with the single infected cell technic of Burnet (1929).