Opioid peptides belong to a group of agents, produced in porcine ovarian follicles, which affect functions of granulosa and theca interna cells. During short incubation of the cells with opioids (µ δ or κ agonists) inhibition of steroidogenesis prevails, while in the presence of LH, trophic agent for these cells (from large follicles), stimulation of steroid hormones under influence of opioids predominates. The mechanism of inhibitory action of opioids on follicular steroidogenesis was investigated using the agonist of mainly µ receptors, FK 33-824.