To clarify the role of the genetic mutations in the clinical course of acute myeloid leukemias (AML), we analyzed for p51, p53, FLT3 and N-ras gene mutations and the expression of the p51 gene in relapsed AML. Paired samples obtained from patients with AML at both stages of diagnosis and first relapse were analyzed. Twenty-four patients with relapsed AML survived for 6 to 81 months (median 24 months) from diagnosis. In one patient, no point mutation of the p51 gene was detected, but loss of the p51 gene expression was observed at both stages. Point mutations of the p53 gene were positive at both stages (+/+) in two patients and negative at diagnosis and positive at relapse (-/+) in two patients. Tandem duplication of the FLT3 gene was detected in five patients at both stages (+/+). N-ras gene mutations at both stages (+/+) were detected in three patients. Mutant p53 at relapse was associated with short survival in patients with relapsed AML (P<0.014). Our findings show that p53 mutations were, at least in part, associated with the mechanism of relapse in AML, while new p51, FLT3 and N-ras gene alterations did not occur at relapse. Loss of the p51 gene expression in de novo AML has not been reported yet.