Nervous, endocrine and immune systems are regarded as a complex functional unit, interacting by their specific chemical messengers – neurotransmitters, systemic hormones and hormone-like mediators of immune cells (cytokines). Cytokines are known to affect several endocrine axes. Interleukin-lβ (IL) was administered in rats intraperitoneally twice daily from day 17 to 21 of pregnancy. Some of the IL-treated mothers were rapidly decapitated 1.5 h after the last injection. The fetuses were delivered by cesarean section. Maternal plasma CRF, ACTH and corticosterone were found to be significantly elevated. Fetal adrenal and thymus weights were lower, and plasma corticosterone did not differ from controls. Fetal plasma testosterone was decreased in males, androstenedione was increased in females. Open-field testing revealed a higher total locomotor activity of IL offspring than of controls. IL offspring showed worse results in Skinner box learning than controls. Sexual behavior was only affected in males, showing a higher percentage of female-type lordosis behavior after castration and estrogen treatment compared to controls. At the age of 6 months responsiveness to ‘novel-environment stress’ of IL groups was significantly lower than that of controls in terms of plasma corticosterone. These results indicate that prenatal treatment with IL-lβ results in long-lasting alterations in psychomotor development, behavior as well as in the neuroendocrine system.