The shape and neuronal number of the inferior olivary complex (IOC) were determined in the water buffalo (Buballus bubalis). The configuration and interrelations of the IOC compartments were ascertained by investigating serial sections through the whole rostro-caudal extent of the IOC. Nissl-stained celloidin sections of six water buffalo's brainstems were used. The IOC in the water buffalo consisted of three major nuclei and four small cell groups. The medial accessory olivary nucleus (MAO) had the longest rostro-caudal extent as well as the highest number of neurons (98,000 +/- 3,000). Although the total area of the principal olivary nucleus (PO) was smaller than the area of the dorsal accessory olivary nucleus (DAO), the PO had the second largest neuronal number. The total number of neurons on both sides of the IOC was 210,000 +/- 7,000 cells. The average neuronal density was 3,000 cells/mm3. Although the size of the PO relatively increases while the size of MAO decreases with the development of the cerebellar hemispheres, the IOC in most mammals maintains a similar structure except for the higher primates and marsupials. The water buffalo IOC showed morphological similarities to the almost all mammalian IOC including rats as follow; the main part of the MAO consists of three subgroups (a, b and c), the DAO is Boomerang-shaped while the PO is a simple U-shaped structure.