The technique of somatic cell hybridization and the concept of tumour suppressor genes share a common history. Somatic cell hybrids between mammalian tumour cells and their normal cellular counterparts invariably are non-tumorigenic, establishing the recessive genetic nature of tumorigenicity. The development of cytogenetics and microcell hybridization has provided methods for localization of the tumour suppressor genes to specific chromosomal regions. Continuing studies of this type will facilitate the isolation of these genes by molecular methods including differential cDNA screening and 'reverse genetics'.