Human neuroblastoma SH-SY5Y cells were used to study the effects of transforming growth factor β1 (TGF-β1) and bone morphogenetic protein 2 (BMP-2) on neuronal differentiation and acquisition of a catecholaminergic phenotype. SH-SY5Y cells express the intracellular factors activated through the receptors of the TGFβ superfamily members, Smad1 and Smad4, as in basal conditions or after differentiation with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or retinoic acid (RA). TGF-β1 and BMP-2 induce differentiation in SH-SY5Y cells by different pathways: the effect of TGF-β1 is potentiated by TPA and the effect of BMP-2 is blocked by RA. Cell differentiation due to TGF-β1 treatment is accompanied by an increase in tyrosine hydroxylase (TH) expression, more pronounced in the presence of TPA or RA and counteracted by BMP-2. BMP-2 and RA both induce noncatecholaminergic cell differentiation, and together they may induce choline acetyltransferase expression in serum-cultured cells. In conclusion, our results suggest that TGF-β1 and BMP-2 may contribute, in opposite ways, to regulation of the neuronal catecholaminergic phenotype.