The axon degeneration following lesions in the dorsal lateral and posterior lateral thalamic nuclei of the cat was traced in serial sections impregnated by the Nauta-Gygax method. The following conclusions were drawn. 1. The dorsal lateral nucleus projects diffusely to the cortex of the middle and posterior suprasylvian gyri, the lower part of the posterolateral gyrus, the anterior and posterior limbic regions, the postsubicular area and the hippocampal fusiform gyrus. However, the severely degenerating cortical areas vary with the site of the lesions in the lateral dorsal nucleus. The anterior part of the dorsal lateral nucleus projects profusely to the anterior part of the above-mentioned cortex, while the posterior part of the nucleus has strong projection to the posterior part of the cortex. This indicates that the cortical projection of the dorsal lateral nucleus is organized essentially in a topical manner in the anteroposterior direction. 2. The cortical projecting area of the posterior lateral nucleus corresponds roughly to that of the dorsal lateral nucleus. In addition, it includes the anterior suprasylvian gyrus and the anterolateral part of the lateral gyrus, area 19. The heavily projecting areas, however, are limited to the anterior and middle suprasylvian gyri and the adjacent part of area 19 in the lateral gyrus, as well as the cortical part around the anterior part of the splenial sulcus. Moreover, the heaviest cortical projection of the posterior lateral nucleus to these cortical areas is organized in a topical manner in the anteroposterior dimension. The anterior part of the posterior lateral nucleus projects most profusely to the anterior part of the heavily projecting areas, while the posterior part of the nucleus has the most massive projetion to the posterior part of the areas. In all cases with lesions in the posterior lateral nucleus slight degeneration is found in the limited cortical part of the anterior sylvian gyrus. 3. It should be mentioned that the dorsal lateral and posterior lateral nuclei have diffuse projection to certain cortical areas, collectively called the association cortex, though their heavy projections are organized in a topical manner in the anteroposterior dimension.