Mycosphaerella fragariae (Tul.) Lindau isolated from several commercial strawberry varieties in different localities varied in cultural characteristics. Each strawberry variety gave rise to a more or less distinct cultural type. Twenty-five cultural types were recognized. Variations were also found among isolates from native F. virginiana in different areas. These variations included differences in colony color, pigment production, rate of growth, topography of colony, and rate of conidial production.Some isolates produced variants in culture on artificial media. Differences in stability were exhibited by different types. Variations or mutations were detected in two cultural types after they had passed five times through hosts other than those from which they were originally isolated.It is postulated that the possible number of distinguishable types of M. fragariae occurring in nature is infinite, being limited only by the possible number of genetic variations in the host itself.