The authors studied the response of enterochromaffin cells (Ec-cells) of the duodenal mucosa of rats during parenteral and intragastric administration of food mixtures containing a fatty emulsion venolipid (Japan) and of food mixtures containing no fat. The food mixture was administered round the clock, uniformly throughout 15 days. The Ec-cells were detected by the argentaffinity method modified by Phontane . It was discovered that during parenteral and intragastric administration of the food mixture containing a fatty emulsion, the amount of the Ec-cells in the duodenal mucosa was 3 times greater as compared with control. There were cells with varying intensity of the argentaffinity response, which attests to an active release of hormones synthesized by the Ec-cells. During intragastric administration of the food mixture containing no fatty emulsion, the status of the Ec-cells was the most similar to that seen in control. This is suggestive of an important role of the diet fat for changes in the Ec-cells. The changes found should be taken into consideration in the assessment of the effects of parenteral and intragastric feeding on the body and intestine and in the choice of the most optimal methods of feeding.