The effect of a bacterial neutral protease on cultured cells was examined with special reference to its activity on the detachment of cells from glass surface, dissociation into single cells and to the inhibitory effect on cell proliferation. Fibroblasts of strains L-929 and CHO-K1, and epithelial cells of strains HeLa-S3, JTC-16 and RLC-10(2) were employed. Fibroblasts were detached and dissociated when this protease was added to MEM supplemented with fetal bovine serum. The epithelial cells were detached but were scarcely dissociated. Kinetic data were obtained concerning the dispersing characteristics of this bacterial neutral protease together with a few aspects on the difference between epithelial cells and fibroblasts in the nature of cell to cell, and cell to substrate interactions.