This work is part of a study investigating the movement of microcystin from aquatic to terrestrial ecosystems via trophic transfer. Little brown bats (Myotis lucifugus), feeding opportunistically on aquatic insects including Hexagenia mayflies, were collected from a maternity roost near Little Traverse Lake (Leelanau County, Michigan, USA). Bats and fecal samples were collected for dietary analysis, quantification of microcystin in livers and feces, and histopathological evaluation of the liver. Liver was collected in RNAlater and stored frozen. Livers from three bats with the highest microcystin levels by ELISA were thawed, washed with PBS, fixed in 10% neutral buffered formalin, processed routinely for histopathology, and assessed by light microscopy. Microscopic lesions included centrilobular congestion, periportal to midzonal hepatocellular vacuolation, and low numbers of portal inflammatory cells. These changes are non-specific; no evidence of acute microcystin toxicosis was present. Results suggest that despite the detection of microcystin in bat feces from the site, there is no evidence of acute clinical toxicity in the bats collected.