We investigated the effect on differentiation of genistein, an inhibitor of tyrosine protein kinase, and 1-(-5 isoquinolinylsulfonyl)-2-methylpiperazine (H7), an inhibitor of protein kinase C, in neuroblastoma cell lines. Growth inhibition and expression of morphological and biochemical properties were examined in the human neuroblastoma cell lines TS12 and SJNKP. Genistein and H7 induced neurite outgrowth, increased acetylcholinesterase activity and cell growth inhibition in both cell lines. These results underline that tyrosine protein kinase and protein kinase C may play a key role in the cona ol of differentiation and proliferation of neural cells.