It has already been accepted that the function and activity of the testis is regulated not only by gonadotrophins, but also by many locally produced factors and by cell-cell interactions. That is why the aim of our work was to determine whether macrophages and/or their products have an influence on Leydig cell steroidogenic activity. The source of Leydig cells and macrophages were male bank voles of spring and autumn generations, reared in 18 light:6 dark or 6 light:18 dark (18L:6D or 6L:18D) conditions for 7-8 weeks. The Leydig cells were growing in monocultures or in co-cultures with macrophages (testicular or peritoneal), either as control or hCG-stimulated ones. To some of the cultures 6 IU/ml of interleukin 1alpha (IL-1alpha) was added. After then the cells were analysed morphologically, histochemically, and radioimmunologically. In the present study we found many differences in morphology and steroidogenic activity of Leydig cells obtained from different photoperiods. Leydig cells from a long day formed monolayer contrary to the cells from a short one growing as single cells or in clusters. Moreover, Leydig cells from a long photoperiod produced more testosterone and were sensitive to the stimulatory effect of both testicular macrophages and testicular macrophage-conditioned medium. They were also more sensitive to the inhibitory influence of IL-1alpha.