The distribution of the Galalpha1-3Gal antigen (Galalpha) in cultured adult porcine islets (API) and fetal porcine pancreatic islet-like cell clusters (ICC) was studied using immunoelectron microscopy. API and ICC were cultured for 1 and 5 days, respectively, and immunogold labeled using human affinity isolated anti-Galalpha1-3Gal antibody, GS-IB4 lectin and antibodies against islet pancreatic hormones, vimentin, and von Willebrand factor. Differentiated endocrine cells were Gala-negative, but, in ICC, some immature endocrine cells were slightly Gala-positive. The Gala-expression in API was much weaker compared to ICC. In both API and ICC, the Gala antigen was expressed on duct epithelial cells, acinar cells, and endothelial cells. In ICC, strong Gala expression was observed on flattened cells covering their surfaces. These cells were identified as centroacinar cells originating from intra-islet ducts. In conclusion, although mature endocrine cells of cultured API and ICC lack the Gala-xenoantigen, several other cellular compounds are strongly Gala positive, which may contribute to xenorejection of these grafts.