The Met-enkephalin-like immunoreactivity was studied in the thalamus of the cat using an indirect immunoperoxidase method. The densest network of immunoreactive fibres and terminals was observed in the epithalamus and the intralaminar nuclei, particularly those located along the midline nuclei interanteromedialis, submedius, rhomboidens and reuniens. The nuclei parafascicularis and centrum medianum contained also numerous immunoreactive fibres and terminals, whereas the lamina medullaris externa had a lower density of immunoreactive terminals. Enkephalin fibres were almost totally absent in the lateral nuclei of the thalamus, and in the posterior group only the magnocellular part of the corpus geniculatum mediale contained some immunoreactive fibres.