Regional blood flow in the myometrium and myomata has been measured during laparotomy in 11 patients using locally injected 133Xenon. Blood flow was calculated from the wash-out curves using both initial slope technique and compartment analysis. Assuming equal partition coefficients in myometrium and myomata the following values in ml ± min−1 ± 100 g−1 are seen: initial slope technique–myometrium 15.6±2.29, myomata 5.1±0.95, compartment analysis–myometrium 20.01±3.21, myomata 5.5±1.16. The blood flow was always lower in myomata than in myometrium of the same uterus. The main reason for the reduction of blood flow per unit weight of uterus in patients with myomata previously reported thus seems to be low blood flow in the myomata. A slight reduction of blood flow in the surrounding myometrium, however, also seems probable.