We studied parameters of iron and copper status in male and female weanling rats that swan 1 1/2 hours per day, 5 days per week or were sedentary for 9 weeks. Final body weights of exercised males were lower (P less than 0.005) than sedentary males, although food intakes were comparable. Blood hemoglobin concentrations and hematocrit levels were increased in the exercising males compared to the sedentary males (P less than 0.025). Serum ceruloplasmin levels were significantly elevated in the exercised group. There was a trend toward decreased iron and increased copper in the spleens, livers and hearts of the exercised males. Total fecal iron was increased and, therefore, apparent iron absorption was decreased in the male exercise group as calculated from an iron and copper balance study conducted during week 8 of the exercise period. In female rats there were no effects of exercise in the parameters measured. Whether the different responses of males and females are due to sexual differences or a relative lack of exercise in the female rats which floated easily is not known. Elevated ceruloplasmin levels may be related to the stress of exercise. The results of this study indicate that exercise produces an alteration in iron and copper distribution and/or iron reutilization, absorption or excretion.