At least 13 of 34 patients with acute myeloid leukemia (AML) of varying FAB types were heterozygous for a BamHI restriction fragment length polymorphism (RFLP) of the Ha-ras gene on chromosome 11. In 4 of these 13 patients, one allele of the Ha-ras gene was deleted. Two of these cases had an informative heterozygosity for an RFLP on the long arm of chromosome 11. Analysis of these cases indicated that loss of genes from chromosome 11 was restricted to the short arm. In three cases with loss of one Ha-ras gene, the remaining gene had no mutations in critical areas of exons 1 and 2. With the exception of one AML case with amplification of MYC, no gross structural abnormalities in 12 other oncogenes were detected.