Muscle blood flow (MBF) was determined in 11 patients on chronic overdoses of ergotamine tartrate and in 12 controls, using the local 133xenon clearance method. The difference in MBFs between the groups was insignificant, 59.7 +/- 21.4 and 61.6 +/- 10.8 ml/100 g/min, respectively. Six patients taking ergotamine in doses exceeding 0.25 mg/kg/week showed a significant (p less than 0.01) reduction of MBF (45.2 +/- 10.7 ml/100 g/min). This reduction could be measured before the manifestation of symptoms or signs of circulatory insufficiency.