THE effects of recombinant ciliary neurotrophic factor (CNTF) on chromaffin cells of the postnatal rat adrenal medulla were investigated and compared with recombinant nerve growth factor (NGF). Adrenal medulla cells were cultured in serum-free media and the survival was assessed by tyrosine hydroxylase immunohistochemistry after 4 days in vitro. While both recombinant NGF and CNTF enhanced the survival and differentiation of chromaffin cells, CNTF at 50–500 ng ml−1 was significantly better than NGF. Furthermore, CNTF was effective at 1.0 ng ml−1, and this effect was blocked with an antibody to CNTF. When the factors were combined, cell survival was also enhanced above the values for either growth factor alone. The highest proportion of cells induced to develop processes (neuronal phenotype) was obtained in the presence of CNTF.