The cutaneous vasodilatation and plasma extravasation observed following antidromic stimulation of trigeminal sensory branches in the rat are reduced by atropine. The atropine-sensitive component does not originate from the seventh cranial nerve (facial nerve) or from the mental nerve, because after chronic section of these nerves an atropine-sensitive component persists. The cholinergic component of the plasma extravasation is abolished by chronic bilateral extirpation of the superior cervical ganglia but this is not the case for the vasodilatation. Our data suggest that trigeminal sensory fibres are not the only fibres involved in these vascular responses seen in the lower lip of the rat after electrical stimulation of the mental nerve.