A restriction fragment length polymorphism (RFLP) for the c-fms gene was identified in the human oral squamous cell carcinoma cell lines, Ca9-22, HSC-2 and -3. The RFLP was detected after EcoR I, BamH I and Hind III endonuclease digestion, indicating the presence of two alleles, a and b. The allele a deleted 426bp length of allele b. We determined the sequence of this deletion, that localized in intron 11 with an EcoR I site. The phenotype of Ca9-22 was aa, and the others were bb. Both phenotypes were equally expressed and the transcripts were phosphorylated in these cell lines. The distribution in the analyzed population (66 patients and normal individuals) was 3.1% homozygotic aa, 13.5% heterozygotic ab and 83.4% homozygotic bb.