Agonist-activated phosphoinositide (PI)-specific phospholipase C initiates PI hydrolysis to produce signals implicated in mitogenic signaling in which the cyclin-dependent cdc2-protein kinase of the maturation-promoting factor is a major protein-tyrosine kinase (PTK) substrate. It has been suggested that PI mitogenic signals are separable into PTK-dependent and non-PTK-dependent by genistein, a tyrosine-specific protein kinase inhibitor. However, we show here that DNA synthesis was abolished in human Chang liver cells although the sulphate-induced PI second messengers, i.e. inositol 1,4,5-trisphosphate and sn-1,2,diacylglycerol, were at equivalent dose-response levels with or without genistein (0.5 mM, 135 microgram/ml). This genistein dosage had been demonstrated to be effective in suppressing tyrosyl phosphorylation in cells. There was no increase in the trypan blue dead cell index. We have shown previously that human Chang cells stimulated by this 'non-growth-factor' agonist, i.e. sulphate, as well as extracellular ATP, became rounded with raised intracellular pH. ATP-induced cell rounding and intracellular alkalinization were not affected by the presence of genistein (0.5 mM). In the present investigation, that genistein dosage had also no effect on these cellular responses when initiated by added sulphate. It seems that the mitogenic signaling function of PI second messengers is dissociable and requires unsuppressed PTK activity.