Glicentin-immunoreactive (GLI-IR) neurons and nerves were studied in the central nervous system of guinea pig. GLI-IR perikarya were found in the medulla oblongata located in the nucleus tractus solitarii, in the nucleus commissuralis, in the nucleus reticularis lateralis and the formation reticularis. Immunoreactive varicosities, however, were seen in many other areas of the central nervous system such as in the hypothalamus, in the nucleus proprius striae terminalis, in the nuclei thalami mediani, in the substantia grisea centralis, in the nuclei raphe, in the formatio reticularis and in the vagus neucleus tractus solitarii-system. Some of the described GLI-IR varicosities may therefore be extensions of the neurons located in the medulla oblongata. Furthermore, the role of GLI as a putative neurotransmitter is discussed.