To investigate the parasympathetic regulation of the endocrine pancreas in spiny mice (Acomys cahirinus), unilateral electrical stimulations of the left cervical vagus nerve were performed in these animals and their controls, the albino mice. Plasma insulin and glucose levels were measured before and after the stimulation. The stimulation parameters were: 2-2.5 V, 14 Hz, 1 msec for the albino mice and 3 V, 14 Hz, 1 msec or 15-20 V, 20 Hz, 1 msec for the spiny mice. Already 2 min after the start of the stimulation, the acomys as well as the albino mice showed a significant increase in plasma insulin levels which was accompanied by a weak but significant increase in glycemia. However, the total insulin output in the acomys mice was half than that of the albino mice. Carbachol administration had no effect on insulin secretion in the acomys mice, while it increased that of the controls. Atropine pretreatment failed to abolish the insulin release elicited by electrical stimulation of the vagus nerve in the acomys mice, while it abolished it in the albino ones. It is proposed that the vagus-nerve mediated insulin release that is present in the acomys mice is exerted, not via muscarinic receptors as in controls, but possibly via other neurotransmitter(s).