During pregnancy, leiomyomas may cause complications such as spontaneous abortion, premature labor, and obstruction of labor. The conventional real-time ultrasound examination usually detects myomas adequately, but, in some cases, a local thickening of the uterine wall persists throughout the examination, interfering with the differentiation between myoma and contraction. In such cases, repeat scanning approximately 30 minutes later differentiates contractions, which usually resolve, from myomas. We examined 10 patients with B mode and color Doppler ultrasonography. In the 5 patients with myoma, we observed splaying of the vessels around the mass, whereas in the 5 patients with contraction, there was no vessel displacement in the area of the local myometrial thickening. The use of color Doppler and observation of these findings may obviate a prolonged ultrasound examination in questionable cases.