Seasonal variations in cause- and age-specific suicide rates in males and females were analysed in Osaka, Japan, for the years 1974–83, using profile analysis. Significant cause differences were found in males: (1) the rate for poisoning by domestic, car-exhaust or other gases was high in winter and spring and low in summer and autumn; (2) the rate for hanging, strangulation and suffocation was low in winter; (3) the rate for a variety of violent methods (chemicals, firearms, drowning, etc.) was high in summer. Similarly, there were sex differences in the variation for causes (2) and (3) and for ages 40–54. No significant age difference was found in either sex. Seasonal differences in the ease of suicidal methods and sex- and season-specific psychosocial factors were thought to be the major determinant of the seasonal variation.