By using the cDNA probe for the human alpha-fetoprotein (AFP) gene, one restriction fragment length polymorphism (RFLP) was discovered in Japanese patients. A variety of combinations of restriction enzymes and probes were evaluated in DNA samples from 25 Japanese individuals who were genetically unrelated. As a result, AvaII identified one invariant band of 8 kb and polymorphic bands at either 2.8 or 2.0 kb with the 5'-region probe from a cDNA clone, pHAF7. With the AvaII/pHAF7 combination, we examined the loss of heterozygosity in 14 patients with hepatocellular carcinoma (HCC). Of 6 informative specimens, 2 showed loss of heterozygosity. These data suggest that the AFP cDNA probe could be useful for analyzing loss of heterozygosity on chromosome 4q in human HCC.