The majority of studies as to whether gastric and nongastric factors are involved in the ' rotation ' of the human embryonic stomach around its longitudinal axis have been morphological. The aim of this study was to analyse, with morphometric support, the influence on the angular modifications during gastric rotation of the simultaneous changes of the gastric walls and mesenteric growth, and the volumes of organs adjacent to the stomach (right, left and posterior groups). Computer imaging techniques were applied on cross sections of a graded series of 10 human embryos (from Carnegie stage (CS) 11) and 2 fetuses. A clockwise gastric rotation occurred during the embryonic period. The most rapid angular modifications took place from CS 11 to 16, after the rotation became oscillatory with angular changes in clockwise and anticlockwise directions, reaching the highest value at CS 18 (at the supraomental part of the stomach : 54.37m ; at the omental part : 68.03m) ; after this period the angular values tended to stabilise. The predominant growth of the left gastric wall over the right and the changes in the width of the gastric mesentery were the most persistent factors involved in the modifications of the transverse gastric angle during the embryonic period although without relationship to their direction. During the increasing angular phases, clockwise rotation was promoted by the decrease of the volume of any group of organs adjacent to the stomach. When the volume of the left and posterior groups increased simultaneously, clockwise or anticlockwise angular directional change was related to the respective decrease or increase adjacent organ volume to the right. We conclude that the stomach of the human embryo undergoes heterogeneous and multifactorial rotation as a consequence of the overall increase in gastric wall growth to the left and the increase of gastric mobility produced by the previous mesenteric enlargement, and that the rotational direction results from the forces exerted on the stomach and the gastric mesenteries by the adjacent organs.