The 3p deletion was first noted by cytogenetic analysis and was later confirmed by several independent studies using restriction fragment length polymorphism (RFLP) probes. As an initial step towards positional cloning (reverse genetics) of the tumor-suppressor gene(s) on 3p, a detailed analysis of the minimum deleted region(s) on 3p was performed with 13 RFLP probes and 48 paired human lung cancer samples. All nine small-cell lung cancer cases (100%) and 31 of 39 non-small-cell lung cancer cases (79%) showed allelic loss at one or more loci mapped on 3p. We show here that three distinct regions on 3p appear to be frequently deleted in lung cancer. These regions include 3p25, 3p21.3 and 3p14-cen. The present study should warrant future work focusing on these chromosomal regions on 3p, and may ultimately lead to the isolation of tumor-suppressor genes involved in the pathogenesis of lung cancer.