Study was begun during the summer of 1969 on the role of substratum and food in the distribution of 5 species of pulmonate snails in Douglas Lake, Cheboygan County, Michigan. Quantitative sampling in the field revealed that the densest populations of Physa sayii crassa were on hard substrata (e.g., stones) in shallow water close to shore; laboratory experiment confirmed a preference for a stony over a sandy substratum. Helisoma antrosa percarinata was most densely populated on sandy substrata, usually in water between 0.6 and 1.5 m deep; preference for a sandy substratum, as well as a tendency to burrow, were demonstrated in the laboratory. Helisoma campanulata was also most densely populated in areas with a substratum of sand. Physa parkeri and Stagnicola emarginata angulata exhibited more complex and varied patterns of distribution. Analyses of stomach contents of field collected snails revealed that all 5 species consume a rather wide variety of plant, animal and detrital material; evidence of selectivity in food habits is at present lacking for any of the species.