Intracellular signalling pathways mediating the effects of growth factors and oncogenes on cell growth and transformation present a challenging new class of target sites for anticancer drug development. Several drugs are already available that may act in this way, including drugs that act on protein serine/threonine kinases, protein tyrosine kinases and phospholipase C, as well as inhibitors of myo-inositol signalling. As our understanding of the signalling pathways involved in growth control increases, new sites for pharmacological intervention will become apparent. Garth Powis reviews the evidence that this approach may eventually lead to new, more selective drugs for treating cancer.