The effects of halothane and sueeinylcholine (SCh) on Vo, and blood flow of the canine graci-lis muscle were determined and compared with previous findings for the gastrocnemius muscle. Because halothane decreased and SCh increased the Vo2's of the two muscles to approximately the same extent, the responses of the two muscles were averaged and used to estimate the contribution of change in skeletal muscle Vo, to change in whole-body Vo,. These projections suggested that increasing halothane from 0.1 to 0.8 per cent would reduce skeletal muscle Vo, approximately 12 per cent and comprise a decrease of 4 per cent in whole-body Vo,. Infusion of SCh, 0.3 mg/kg/min, was estimated to increase skeletal muscle Vo, approximately 30 and 14 per cent during the first and second hours, respectively, and to contribute increases in whole-body Vo, of 11 and 5 per cent, respectively. The accuracy of the latter estimates was supported by previous direct determinations of the effects of SCh on whole-body Vo,. Whereas the gracilis and gastrocaemius muscles were similar in these responses, actual resting Vo, and blood flow were significantly less for the gracilis muscle, as were cytochreme e concentration, succinic dehydrogenase activity, and Vo,in citro.