Laboratory investigations suggest that the effects of weather on avian reproduction could be manifest via a "stress" response resulting in an elevation of circulating levels of corticosterone and a depression of reproductive hormone secretion. However, field investigations indicate that additional endocrine responses also occur. Inclement weather early in the breeding season, i.e., before the nesting phase has begun, is generally not stressful in terms of plasma levels of corticosterone but does result in a delay of gonadal maturation and decreases in circulating levels of LH and sex steroid hormones. Conversely, storms that strike after the nesting phase has begun and when adults are feeding young do appear to be stressful, resulting in an increase in corticosterone and loss of body weight, but do not affect plasma levels of LH and sex steroid hormones. This latter fact is thought to be highly adaptive because the reproductive apparatus is maintained in a functional state so that renesting can begin immediately when environmental conditions improve. These data indicate that two endocrine mechanisms may be important for regulating responses to inclement weather under natural conditions.