Considerable evidence suggests that the E2F/DRTF1 family of transcription factors (hereafter referred to as 'E2F') plays a critical role in cell growth control. For example, the ability of several small DNA tumour viruses, such as SV40, adenovirus and human papillomavirus, to transform certain cells is tightly linked to their ability to deregulate E2F. Furthermore, E2F appears to directly regulate the transcription of a diverse set of genes implicated in DNA replication and cell growth control. Finally, a number of known cell cycle regulators, some of which are commonly mutated in human tumours, appear to exert their effects, at least in part, by altering E2F activity. Among these are pRb, p53, cdk-2, cdk-4 and certain cyclins.