A formula to estimate ground level UV-B from meteorological data was developed for the purpose of utilization in ecologic and/or environmental epidemiologic studies. Estimated values were obtained for various regional points in Japan. There was a very high correlation (r = 0.98) between estimated and observed values at four weather stations during 1991-93. Ranks of the UV-B level for the 1990 year mean and decennial period means during 1961-1989 approximately equated ranks of latitude. However, > or = 10% variation in period means or > or = 10 difference in rank was observed at several regional points. Estimated UV-B level is affected by meteorological conditions including solar radiation and total ozone, and may serve as a refined and improved exposure index compared to conventional indices used in prior studies.