In this letter to the editor, the authors discuss their study of the effect of latitude on suicide rates in Japan, given that there is a northern predominance in the prevalence of seasonal affective disorders in Japan. Government statistics on suicide for 1999 were examined & variables associated with latitude effect, yearly mean temperature, & yearly total sunshine were analysed. Yearly mean individaul income & yearly unemployment rates for each prefecture were also included. Yearly total sunshine was the only individual variable to predict significant variance in suicide rate. (5 refs.)