The acaricide chlordimeform has been reported to have adverse effects in mammals that may be mediated by an interaction with alpha-adrenergic receptors. Since the hormonal signals involved in the regulation of reproductive function are themselves under hypothalamic adrenergic control, the study was designed to investigate the effects of acute exposure to this compound on the hypothalamic-pituitary-testicular axis. Male rats given two intraperitoneal injections of chlordimeform-HCl (20 or 50mg/kg) spaced 12 hrs apart showed 24 hr declines in serum gonadotropins at 50mg/kg that were paralleled by a drop in testosterone. These changes returned to control levels by 96 hrs. Thyroid stimulating hormone exhibited a dose-response decline that was accompanied by a similar decrease in serum thyroid hormone levels. The stimulated secretion in vitro of gonadotropin-releasing hormone from hypothalamic explants was suppressed at the higher dose, while LH release from pituitary fragments in culture was unaffected. (Copyright (c) 1990 by Academic Press, Inc.)