The study was undertaken to determine the effect of histamine on blood flow to the ovary and oviduct in the domestic hen (Gallus domesticus). Cardiac output and blood flow were measured with 86RbCl through the ovarian stroma, white ovarian follicles, yellow preovulatory follicles, postovulatory follicles and four oviductal parts: infundibulum, magnum, isthmus and shell gland 1 min and 5 min after histamine treatment. In comparison with control hens which received 0.9% NaCl, histamine significantly increased (by 21.4%) cardiac output exclusively 5 min after its treatment. Blood flow (ml/min/g tissue) through the stroma, the infundibulum and the shell gland was significantly elevated both 1 min (54.3%, 84.3% and 64.2%, respectively) and 5 min (87.1%, 111.5% and 70.4%, respectively) after histamine administration and through the ovarian follicles (29.3%-61.9%) exclusively 5 min after histamine treatment. The increase in blood flow through the ovarian stroma, follicles and the oviductal parts following the administration of histamine was not the result of increased cardiac output but the consequence of local histamine action on blood flow through the ovary and oviduct. The results of the present study indicate that histamine, by influencing the hemodynamics of blood vessels and in consequence changing the blood flow through the reproductive organs, participates in the processes taking place in the ovary during growth, maturation and regression of the follicles, and in the oviduct during formation of the egg.