The incidence of secondary myelodysplastic syndromes (MDS) are rarely reported in an homogeneous patient population treated for non-Hodgkin's lymphoma (NHL). Less than 10 per cent of secondary MDS are usually observed in patients treated for Hodgkin's disease and NHL. Data on the incidence of secondary MDS induced by modern chemotherapeutic regimens is needed. Between January 1985 and January 1989, 20 patients with localized gastric non-Hodgkin's lymphomas (stage I to IIE) were prospectively treated at the Institut Gustave-Roussy with PROMACE-MOPP multi-agent chemotherapy and involved-field irradiation. The mean age was 54 years (range 23 to 69 years). Seven patients died while on therapy or relapsed 2 to 28 months after therapy. Thirteen patients were followed up for at least 5 years. Three of the 13 long-term survivors (23 per cent) developed a myelodysplastic syndrome (MDS) 48, 62 and 72 months after the end of therapy. Cytogenetic analysis was performed in two cases and showed-7 and 18q- in one case, t(9;21)(q13;q22), 21q+, i17q in the other case. PROMACE-MOPP plus radiotherapy should not be recommended in patients with localized gastric non-Hodgkin's lymphoma due to the high risk of developing secondary myelodysplastic syndromes.