Ultrasonic real-time B-mode technique was used to record fetal breathing movements (FBM) in 100 consecutively examined women in late pregnancy. During the “inspiratory” phase of the FBM cycle, the diaphragm of the fetus contracts and moves in caudal direction. The diaghragmatic movement is accompanied by a retraction of the thorax with maximum inward movement of the lower sternum and by an expansion of the fetal abdomen. During “expiration” all structures return to their initial position. The incidence of FBM found in 24 pregnancies with various disorders was significantly lower than that in the 76 uncomplicated pregnancies (P < 0.001). In 92% of the observations in which FBM were present for more than 5 minutes within 30- minute recording, this finding indicated an unaffected pregnancy at the time of the examination. No correlation was found between the FBM results and the subsequent course and outcome of the pregnancies.