Hong Kong Chinese patients with myelodysplastic syndromes were screened for the presence of N-ras mutation by using the polymerase chain reaction/dot blot hybridization technique. Three of 20 (15%) cases studied were found to harbour mutant N-ras in the bone marrow mononuclear cell population. One case of refractory anaemia with excess of blasts and with excess of blasts in transformation had substitution of arginine for glutamine at codon 61. A second case of refractory anaemia with excess of blasts had substitution of serine for glycine at codon 12. In this patient, mutant N-ras was detected in a follow up sample taken two months later although there was no change in the blast percentage compared with the presentation sample. Our study showed that N-ras mutation is an infrequent finding in Hong Kong Chinese myelodysplastic syndrome patients. An N-ras mutation is not necessarily accompanied by an alteration in the haematological picture.