The MDM2 gene is a gene whose product binds to p53 and regulates its function. Amplification of MDM2 has been found in human sarcomas, where it leads to inactivation of p53. In 64 cases of generally advanced myelodysplastic syndromes, we found no amplification or rearrangement of MDM2 gene by Southern analysis. MDM2 RNA was also normal in the 15 cases where Northern analysis was made. Thus, amplification of MDM2 is not seen or must be very rare in myelodysplastic syndrome (MDS). Because P53 gene mutations are not frequent in MDS, inactivation of p53 seems to be, overall, a rare pathogenetic event in MDS.