The purpose of this study was to ascertain whether there are any socioeconomic or environmental factors possibly contributing to childbirths related to sex. Using the vital statistics issued by the Kagoshima prefectural government, secular changes in sex ratio at births were studied over a 20-year period 1968 to 1987. The relationships between sex ratio at births and the indicators of selected socioeconomic conditions or the measures of some ionic concentrations in drinking water were also examined among 96 local community units (city, town and village) in Kagoshima prefecture . The following results were obtained: 1) The sex ratio at births has slowly and progressively declined in Japan as a whole in the course of a 20-year period 1968 through 1987, the decrease being from 1.071 in 1968 to 1.058 in 1987. The sex ratio at births in Kagoshima prefecture, however, has shown a slightly increasing tendency rather than a decreasing tendency over the same study period, although it was generally below the levels in Japan as a whole. 2) A progressive decline in gross fertility rate by the passage of the year was observed in Japan as a whole during the period 1968 through 1987. Similar trend has occurred in Kagoshima prefecture, although the rate was always above the levels in Japan as a whole. The declining fertility appears to have played a role in the decline in sex ratio at births. 3) The values of sex ratio at births differed considerably among the 96 local community-based aras (city, twon and village), the highest, 1.457 was for Mishima village and the lowest, 0.819 was for Toshima village. Both of these two villarges were on the solitary islands and sparsely populated. 4) Of seven indicators of socioeconomic condition (percentage of junior childbearings, percentage of senior childbearings, percentageof girls who enter senior high schools, gross fertility rate, crude birth rate, percentage of primary industries and gross income) studied, only the percentage of senior childbearings was inversely correlated with sex ratio at births. Also, of seven ionic concentrations in drinking water (Na, K, Mg, Ca, Cl, SO4 and CO3), Na, Cl and SO4 were positively correlated with sex ratio at births.
