A single-transducer mechanical sector scanner was used to examine the first-trimester fetus. Fifty-six examinations of 31 patients demonstrated an orderly developmental progression of fetal activity beginning with beating of the fetal heart (7 weeks), progressing ot fetal trunk movement (8 weeks), and culminating in individual fetal limb movement (9 weeks). The mechanical sector real-time scanner is capable of providing a high-resolution image of the first-trimester fetus and the earliest fetal movements.