Fruit bats Rousettus aegyptiacus were depleted of vitamin B12 by exposure to the gas nitrous oxide (N2O-oxygen, 1:1 v/v) for 57-80 days. Conduction velocities along the fastest fibres of the ulnar nerve, as well as the first and second peaks, were similar in control and vitamin b12 depleted animals. It is concluded that neurological impairment resulting from depletion of vitamin B12 by N2O does not involve significant impairment of ulnar nerve function in this species.