In order to obtain fundamental information about the electrostatic effect of microcarriers on fibroblastic cell growth, the aminated poly(gamma-methyl L-glutamate) and the cross-linked poly(epsilon-lysine) beads were prepared. When the growth of mouse L cell on the various beads were determined by common cell culture methods, it strongly depends on the apparent pK(a) of the beads but not on their amino-group content. The polymer beads with neutral apparent pK(a) (7.4-7.6), just as in the physiological environment, were found to be excellent microcarriers, showing the highest growth of fibroblastic cells.