A slice preparation of the cat thalamus containing the lateral geniculate nucleus and the terminal portion of the optic tract is described. Ultrastructurally the slices remain relatively normal for only a short time after cutting. Indeed most cellular elements deteriorate quickly with time but patches of relatively intact tissue were still present even 10 h after cutting and maintenance in a storage bath. However, for 4-5 h after cutting long-lasting intracellular recordings of high quality and stability were obtained, and intrasomatic injection of horseradish peroxidase used for the morphological identification of recorded neurones as X or Y cells.