Melatonin was administered at the dose of 1,2 mcg per capita (an equivalent to pediatric dosages) at days 1, 3 and 5 postpartum to 129/Sv mice, which were followed thereafter till their natural deaths. In adult males, findings included a decrease in body weight and an increase in the contribution of pulmonary lesions, which were revealed upon postmortem examinations, to the overall mortality. In adult females, no changes in body weight occurred, the proportion of middle- and late-age mice having irregular estrous cycles increased, and mortality associated with uterine hemangiomas was accelerated. Trends in malignant tumor yields were different: a decrease in males and an increase in females. Tends in survival patterns were expressed as significant increases or decreases in the lifespans of the last 25% and 10% of male or female survivors respectively. An analysis of the complete survivorships curves in terms of the Gompertz model showed that changes in the initial mortality and aging rate were within the limits determined by the artifactual component of the Strehler-Mildvan correlation between these parameters. On a whole, the trends found in the present work were opposite in males and females being mostly favorable for the former and adverse for the latter. Gender specificity should be kept in mind upon considering the use of melatonin by children and their mothers.