The contribution deals with the histoenzymological makeup of telencephalon and diencephalon of a microchiropteran bat which is considered to have a primitive type of brain. Three esterases, namely acetylcholinesterase (AChE), butyrylcholineesterase (BChE) and nonspecific esterase (NSE), have been studied. In comparison with other mammalian brains the telencephalon and diencephalon of the bat demonstrate a high concentration of enzyme, especially in the nucleus caudatus and putamen, stria medullaris and the nuclei of the thalamus. AChE concentration is higher in neurons, while BChE is seen in almost all fibrous areas of the telencephalon and diencephalon. NSE activity is prominent in neurons and neuropil of neocortex, thalamus and hypothalamus. All the above data indicate that the brain of echolocating microchiropteran bats is metabolically much more active than that of other mammals. This is specifically true of the auditory system which is considerably specialized in these animals; this is also confirmed by the present histoenzymological study.