The presence and distribution of serotonin-containing cells in the gas
troenteric tract of horses have been investigated. The enterochromaffi
n (EC) cells have been identified using immunostaining procedures at b
oth light and electron microscopic level. The EC cells were very numer
ous in the pyloric gland region, were only few in the duodenum but wer
e absolutely lacking from the more distal portions of the intestine.