The distribution of receptor sites for concanavalin A (Con A) on the cellsurface of human gastric cancer cell line (MGC 80-3) and fibroblast cell cultures wasstudied with electron and light microscope after application of Con A-peroxidasemethod.The cytochemical reaction of the majority of non-prefixed MGC 80-3 cellsshows a striking tendency to be more uneven distribution than on fibroblasts.Clustering,patching and capping of Con A binding sites on the cancer cells anduniform distribution on the fibroblasts were observed.The effects of incubationtemperature,prefix treatment,different phase of cell cycles and cell growth condi-tions on the distribution of Con A receptor complexes were observed.The possiblereasons for the more irregular distribution of the cytochemical reaction product onthe MGC 80-3 cells than the fibroblasts are discussed.