Retinoic acid ( RA) inhibited proliferation of cultured human keratinocytes. Southern blot analysis at 24 h showed that RA inhibited nerve growth factor ( NGF) mRNA synthesis in a dose-dependent manner. However, RA stimulated the production of NGF protein up to 187% of control after 96 h and the treatment of cells with RA did not enhance apoptosis, either in the presence of low or high concentration of Ca2+, when compared to the control with DMSO.