We have recently developed a novel in vitro SPF evaluation method with a high correlation coefficient (r=0.93) to in vivo SPF values(test sunscreen formulas : cress m, foundation). In this method, the in vitro SPF value was determined by the ratio of the time taken to achieve the minimal erythema dose with and without the sunscreens applied. We also reviewed the dilution and thin-layer methods for in vitro SPF evaluation, and investigated the relationship between irradiance(3$ imes$10-3 2.5x 10-5W/cm2) and the degree of erythema. The degree of erythema was similar if t he radiation exposure(40mJ/cm2) was kept constant. It was obtained more than 0.90 correlation coefficient when it was compared the results by our new method with those from SPF-290 analyzer (Optometries, U.S.A.).