Geranium (Pelargonium hortorum Bailey) protoplasts were obtained from haploid callus tissue from anther cultures after 3 h of incubation with 2% cellulase (Onozuka SS) and 0.2% pectinase in Murashige and Skoog (MS) medium. The protoplasts were washed and incubated in conditioned MS medium supplemented with 0.1 M mannitol and 0.01 M sucrose in microcultures. The amount of cell wall material deposited on the surface of the living single protoplast was measured with the polarizing microscope and photovolt meter. The refracted light was measured as arbitrary units of photovolts every 12 h. The cell wall regeneration was detected after 24 h of incubation. Maximum deposition of cell wall cellulose material was achieved after 60 h and measured 18.4 photovolt units for cells with diameter of 20 to 40 microns (μ) and 22 photovolt units for cells with diameter of 41 to 60 μ. Mitotic cell divisions started in 12 out of 174 reconstituted cells at the 4th or 5th day of incubation. After nuclear division, new cell wall material deposited on both sides of the isotropic middle lamella. Cytokinesis was completed after 15 h. Twelve colonies, which stayed alive for 2 months, were produced from single protoplasts in microcultures. This is the first attempt to quantify the progressive cell wall material deposition on the surface of living plant protoplasts.