Bacterial toxins are widespread in the environment as well as in the digestive system of humans and animals. Toxin from Gram-negative bacteria (endotoxin or lipopolysaccharide; LPS) has a life-long programming effect on reproduction in rats, but the mediators have not been well-documented, so we investigated the effects of LPS on the timing of puberty in female rats. Because the levels of nitric oxide (NO) and interleukin 1 beta (IL-1 beta) increase following injection of LPS, we injected neonates (post-natal day (pnd) 7) with LPS, with or without NO or IL-1 beta inhibitors. Half of the prepubescent (pnd 30) animals received an additional LPS injection. Vaginal opening, number of ovarian follicles, and serum anti-LPS antibodies were determined. A single LPS injection was sufficient to reduce the primordial follicle pool, but puberty was delayed when rats received 2 LPS injections (at pnd 7 and 30). NO or IL-1 beta inhibitors improved both of these parameters, suggesting that the early detrimental effects of LPS on puberty and primordial follicle pool are mediated by NO and IL-1 beta.