Mechanical stimulation of the mucosa of the proximal colon evoked a hyperemia which also could be elicited when severing the autonomic fibres to the colon. Mechanical stimulation of the distal colon produced a hyperemia which, on the other hand, was abolished by cutting the pelvic nerves. Afferent pelvic nerve stimulation evoked a response similar to that seen when stimulating the distal colon. Adrenergic and cholinergic receptor blockers did not affect the studied colonic vasodilations. Dihydroergotamine, given in doses abolishing the vascular effects of i.a. injected 5-hydroxytrptamine, abolished the hyperemia to mechanical stimulation of the proximal colon but not that of the pelvic stimulation. It is concluded that a local nervous vasodilator reflex exists in the proximal colon similar to that earlier demonstrated in the small bowel (Biber et al. 1971) and that the reflex vasodilatation evoked by mechanical stimulation in the distal colon is mediated via the pelvic nerves. Hence, the vascular control differs in the proximal and in the distal parts of the colon.