In order to determine the number of ganglia and ganglion cells of the myenteric plexus in a hypertrophic segment of the gut a partial surgical obstruction was carried out in the colon of 10 adult rats. The myenteric plexus was studied in "spread" preparations in which the circular and longitudinal muscle layers were intact. With the colon distended and stretched above the surgical obstruction, the muscle layers became intensely hypertrophic and, as a consequence, the surface of the hypertrophic colon increased by 39%. The decrease in number of ganglia and ganglion cells per area in the hypertrophic colon was 37.6% and 36.4%, respectively. The increase of the surface of the hypertrophic colon was proportional to the decrease In number of ganglia and ganglion cells per area. Therefore there was no change in the absolute number of ganglia and neurons in the colon above the partial obstruction. The results of the present study do not support the view that immature cells develop into ganglion cells in the hypertrophic intestine above a surgical obstruction.