A primary culture of thalamic cells from 6-day-old postnatal rats was co-cultured for 6 days with neocortical or cerebellar cells (neurons and astrocytes) from the same litter using a Transwell mesh system. The survival of thalamic neurons grown on the lower well, which were affected by substances released from cells grown on the upper wells, was remarkably promoted by both neocortical co-cultures (target for thalamic projection neurons) and cerebellar co-cultures (non-target). When the cells were seeded on mesh at lower density, the neurotrophic effects of neocortical co-cultures on thalamic neurons (204% of control) were significantly greater than those of cerebellar co-cultures (138%). When the cells were seeded on mesh at higher density, the effects of cerebellar co-cultures increased dramatically (517% of control), while the neurotrophic effects of neocortical co-cultures did not change. Morphologically, the survival of multipolar-shaped thalamic neurons was remarkably improved, as compared to the survival of monopolar, bipolar, and tripolar-shaped thalamic neurons. Basic fibroblast growth factor slightly promoted thalamic neuronal survival (136%), whereas nerve growth factor had no effect. These results suggest that neocortical and cerebellar cells release diffusible factor(s) that promote the survival of specific subpopulation of thalamic neurons, and that at least one of the non-target cerebellar cell-derived factor(s) might be more potent than those released from target neocortical cells.