Genetic effects of pyrex-filtered sunlamp irradiation (primarily UV-B, lambda approximately 280-320 nm which is present in natural sunlight) were studied in diploid and haploid yeast strains designed to monitor the incidence of mitotic crossing over, mitotic gene conversion and mutations. Exposure to UV-B was found to be very effective in inducing all three types of genetic endpoints. These effects could be observed even after UV-B treatments resulting in no cellular inactivation. Comparative studies using filtered sunlamp radiation and germicidal UV radiation (lambda approximately 254 nm) indicated that, at an equivalent survival level (including exposures causing little or no cell death), UV-B induced more gene convertants and that the kinetics of mutations induced by the two lights are demonstrably different.