Sporozoa of the genus Haplosporidium have been found in the liver of snails collected in the vicinity of UMBS. It is an interesting parasite because of the liver damage observed and the lack of host-specificity. It is widely distributed in the area studied with the following recoveries of infected snails: Lake Michigan near Cross Village, 3 of 13 Physa were infected; Lake Huron east of Cheboygan, 3 of 27 Physa; Presque Island, 30 of 40; Black Lake in Chebogyan County, neither of 2 Physa, 1 of 14 Heliosoma, 1 of 19 Stagnicola. No infections were recovered from 3 Physa and 8 Lymnaea from Long Lake in Cheboygan County, or 12 Stagnicola from the beach of Bois Blanc Island. Infected snails were distributed as follows in Douglas Lake: Deer Point at one end of the lake’s greatest length produced 7 Heliosoma, 14 Stagnicola and 16 Lymnaea that were uninfected at a season when infection was very high on Sunny Strand, southwest of Deer Point, 15 of 26 Stagnicola infected, and in Maple Cove, over the peninsula, 3 of 13 Physa and none of 16 Lymnaea were infected (October 1958); South Fishtail Bay had 4 of 16 Physa, 6 of 20 Heliosoma, none of nine Amnicola and none of 25 Campeloma infected (July 1959). The Haplosporidium was recovered in Stagnicola, Physa and Heliosoma but in none of the Lymnaea and Campeloma.