Chromosome 3p is consistently deleted in lung cancer, oral squamous cell carcinoma, and renal cell carcinoma, and is believed to contain several tumor suppressor genes. We have shown a role for chromosome 3 in tumor suppression by microcell-mediated chromosome transfer experiments. We have isolated a gene that is located at 3p21.3 within the smallest region of deletion overlap in lung tumors and is the human homolog of the ribosomal protein L14 gene (RPL14). The RPL14 sequence contains a highly polymorphic trinucleotide repeat array which encodes a variable-length polyalanine tract. Genotype analysis of RPL14 shows that this locus is 68% heterozygous in the normal population, compared with 25% in non-small cell lung cancer (NSCLC) cell lines (p = 0.008). Cell cultures derived from normal bronchial epithelium show a 65% level of heterozygosity, reflecting that of the normal population. Squamous cell carcinoma of the head and neck (SCCHN), which has the same risk factors as lung cancer and is hypothesized to have a similar etiology, demonstrates 54% loss of heterozygosity at the RNA level, suggesting that transcriptional loss may be a primary mechanism of RPL14 alteration in SCCHN. In addition, RPL14 shows significant differences in allele frequency distribution in ethnically-defined populations, making this sequence a useful marker for the study of ethnicity-adjusted lung cancer risk.