OBJECTIVE The homozygous inactivation of tumor suppressor genes is a common event in the multistep process of tumorigenesis. The identification of most tumor suppressor genes known to date has come from the study of individuals with a defective copy of such a gene that increases their predisposition to malignancy. Although much is still to be learned about the function of these genes, they all seem to play a role in cell growth regulation. Karyotypic and molecular studies of several solid tumors suggest the presence of at least three tumor suppressor genes on the short arm of human chromosome 3. We present an overview on the progress made in the identification of tumor suppressor genes involved in solid tumor development. CONCLUSIONS The explosive effort to map the human genome fueled by the Human Genome Project will facilitate the identification of tumor suppressor genes on chromosome 3 and on other chromosomes within the next 2 to 3 years. This information will not only provide a better understanding in cell cycle regulation and differentiation but also new insights in the design of new therapies for the treatment of human cancer.