Using PCR and direct sequence methodology, 19 haematologic malignancies with trisomy 8, 18 with t(8;21)(q22;q22) and 8 with inv(16)(p13q22) were screened for NRAS mutations. Of the 45 samples analyzed, 4 (9%) had a mutation; both wild-type and mutated alleles were observed in these 4 cases. Three of the mutations (involving codons 12 and 13) were found in the trisomy 8 group and 1 (codon 61) among the inv(16) samples. No specific clinical similarities were found in the 3 patients with +8 and NRAS mutation. By analyzing two sequential samples from the patient with inv(16) and NRAS mutation, it was shown that the mutation had occurred after the inversion. Since no NRAS mutations were detected among the t(8;21) samples and only 1 was found in the inv(16) group, we conclude that acute myeloid leukaemias with t(8;21) or inv(16) generally arise and progress without the involvement of NRAS mutations.