Male physical education students were subjected to electrical stimulation for a period of 21 days. The stimulation was performed with alternating currents of rectangular wave form. Group I was stimulated with a frequency of 50 Hz, group II with a frequency of 2000 Hz. Before and after the experimental period, biopsies were taken from the m. gastrocnemius. The muscle fiber size and the number and size of nuclei was estimated at the light microscopic level using stereological methods. The fiber size was significantly increased only in group I. The nuclear number and the nuclear size increased significantly in both groups leading to a higher nuclear volume per unit tissue volume. It was assumed that the proliferation of nuclei is correlated to satellite cell proliferation resulting probably in hypertrophy or hyperplasia of electrostimulated skeletal muscle.