Applying the NADH technique in the myenteric plexus' collum of young and aged guinea pigs, we have studied the morphology of ganglions and neurons, the number and arrangment of neurons and the profile area of neuronal bodies. Ganglions preferentialy elongated or without a defined morphology were observed in five collum segments (proximal, intermediate proximal, medial, intermediate distal and distal). There were no important differences in this aspect from one segment to another, whether in the same age group or between the two studied groups. It has also been observed the presence of relatively small ganglions containing a reduced number of neurons and big ganglions containing a high number of these cells. The neurons were more compacted in the ganglions of the individuals from the younger group, while the majority of ganglions from the individuals of the aged group were more equally divided. Neurons mainly roundish and oval were found in both groups, neurons with the cytoplasmic contour greatly altered could be observed in various ganglions of aged animals. Concerning the area of cellular profile, the majority of neurons of both groups were found in the interval between 101 and 300 µm². Based on the determination of the fragment's area of each collum division, the density of neurons for cm² was estimated, as well as the total neuronal density, in which the individuals of the aged group was aproximately 46% smaller than that of the individuals from the younger group