An enzyme-linked immunoadsorbent assay (ELISA) has been used to study the relative expression of the nerve growth factor receptor (NGF-R) in PC12 cells. Both nerve growth factor (NGF) and fibroblast growth factor (FGF) were found to induce time-dependent increases in receptor expression. The former response was half-maximal at approximately 2 ng/ml and maximal at 25-50 ng/ml. The induction of NGF-R expression by NGF was associated with an increase in the relative level of a 3.8 kb mRNA species encoding this protein. Whereas the induction of the NGF-R by NGF and FGF were both fully inhibited by cholera toxin and cordycepin, the responses were differentially inhibited by the kinase inhibitor K-252a.