This study reports metabolic, body and endocrine organ weight differences between a recessive mutation whirler, and its normal heterozygote. The whirlers, a waltzing mice mutation, are extremely restless, nervous, and excitable. They show syndromes of rapid circling locomotor activity, head-shaking and deafness. 0 2 consumption and metabolic rates of female mice were studied at ages up to 14 months. The two groups of homozygous and heterozygous whirlers were autopsied at three and one-half, ten and eighteen months of age for body and organ weight analyses. At all age levels, either significant or marked decreases were noted in the body weights of the whirler mice compared to the normal heterozygotes. Significant increases were observed in the adrenal weights accompanied by significant decreases in the thymic weights. 0% consumption and metabolic rate analyses demonstrated significant or marked increases in whirler metabolic rates at all age periods. The whirler ovarian and uterine weight changes suggest delayed gonadal function. The data indicate consistently increased metabolic and adrenocortical activities during the life span of the whirlers. The thyroidal and gonadal weight alterations at the various time periods suggest age-related changes which may also be a function of acute and chronic states of heightened adrenocortical activity.