<正> The characteristic distribution of calcitonin gone-related peptide（CGRP）inthe small intestine of rats and its changes in acute intestinal radiation sickness（AIRS）were studied with immunocytochemistry（whole mount stretch preparations of the smallintestine and cryostat sections）and radio-immunoassay.It was found that in all the lay-ers of the intestinal walls

there were large amounts of CGRP immunoreactive（CGRP-I）nerve fibers which existed in especiaUy high density in the myenteric

submucosal andmucosal plexuses.There was also a rather high density of the nerves around the smallvessels of the small intestine and the intestinal crypts.Some CGRP-I neurons were seenin the myenteric and submucosal plexuses.In AIRS

the intestinal CGRP showed a dip-hasic change

in a lower level in the 24th h and a higher level in the 48th and 72nd h af-ter irradiation.The results indicate that CGRP may be related to the regulation of the motility

se-cretion

absorption

sensation

and regional blood flow of the gastrointestinal tract.Pro-bably

CGRP is released under the stress of AIRS and participates in the mechanism ofinjury through many ways especially through the influence on the regional blood flowand the increase of the permeability of blood vessels.