To assess the predictive role of bone marrow culturing in MDS in vitro data of 205 patients were correlated with progression to AML and survival. Both in vitro growth pattern and in vitro differentiation were significantly predictive for progression to AML. Other predictive parameters were FAB classification and the presence of cytogenetic abnormalities in all metaphases analysed. Since FAB classification and in vitro bone marrow culturing appeared confounding variables, the in vitro data were analysed for high risk patients, RAEB and RAEBt and low risk patients, RA and RARS. In 91/110 RAEB(t) patients the estimated chance to develop AML was 25% in cases of normal growth versus 62% if abnormal (p < 0.06). In 82/87 RA(RS) patients the estimated chance to develop AML was 5% and 40% respectively (p = 0.0004). After AML progression median survival was only 2 months (0-16.1 months). In RAEB(t) patients bone marrow culturing did not discriminate for better survival, although a trend was shown. The estimated median survival was 16 months if growth was normal versus 8 months if abnormal (p = 0.07). In RA(RS) patients the median survival also was not significantly different, 31 versus 22 months respectively (p = 0.39). However, if in vitro growth and differentiation were both normal a significant difference in median survival was observed, 35 versus 22 months (p = 0.016). In conclusion, in vitro bone marrow culturing has predictive value for AML development in RA(RS) patients. In RAEB(t), due to many patients dying early in cytopenia, the predictive value is less pronounced. Especially normal growth in RA(RS) patients makes progression to AML very unlikely and these patients should be considered for a supportive approach. In RA(RS) patients with normal growth and differentiation (about 25% of all patients) in vitro bone marrow culturing also predicts a better survival.