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The Sr-87/Sr-86 ratios in monthly precipitation in the forested basin at Kawakami, central Japan, varied seasonally from 0.709 to 0.711 in spring to as low as 0.7062 +/- 0.0004 in autumn over nine years from 1987 to 1995. The seasonal variation can be explained in terms of the mixing of three sources of Sr: sea salt (Sr-87/Sr-86 similar to 0.70917), soluble eolian minerals originating from deserts in continental Asia (similar to 0.711), and biogenic materials growing on soils derived from the volcanic rock substrates in the vicinity (similar to 0.706). It is estimated that the contribution of sea-salt Sr into the Kawakami rain Sr is relatively constant (10 +/- 5%) and that more than half of the Sr is of biogenic origin throughout the year except during spring rains when 50% of the Sr is due to the dissolution of Ca-minerals from Asian dusts. The dominant contribution of eolian components to spring rains is consistent with the high concentration of H-3, which is typical of air masses from Asia. (C) 1997 Elsevier Science Ltd.