Fundamental studies of treatment effects for Hyperpigmented skin lesions by Ruby laser irradiation were carried out using black colored guinea pigs. Biopsy samples till 6 days after irradiation were observed with irradiation condition of pulse widths of 150 μsec-2msec and energy densities of 4.6-20 J/cm2. The threshold curve in the relation of pulse width vs energy density for selective destruction of superficial layer were estimated. The mechanisms of selective destruction of melanosome and superficial layer were discussed and the correlation with the treatment effect were considered
