A retrospective study was carried out in order to investigate the phenotype of fetal haematopoietic progenitors circulating in the maternal blood of seven aneuploid pregnancies. Five of the blood samples were taken during pregnancies affected by various fetal aneuploidies, while the other two were collected after therapeutic abortion due to prenatal cytogenetic diagnosis of trisomies 21 and 18. Haematopoietic progenitor cells, isolated by labelling the erythropoietin receptors with the biotinylated ligand before magnetic sorting and/or fibronectin cell adhesion assay, were cultured in a suitable semisolid medium. Single- or dual-colour fluorescence in situ hybridization (FISH) was utilized to identify and enumerate fetal cells amplified in culture. Fetal trisomies were confirmed in the FISH analysis with chromosome-specific probes in all the cases analysed. The fetal purity rate ranged from 16 to 26 per cent. Haematopoietic progenitors of fetal origin were found to include CFU-E, CFU-GEMM, and possibly also M-BFU-E. Interestingly, a more immature progenitor with high self-renewal capacity (CFU-blast cell) isolated by fibronectin sorting was shown to have a relatively high frequency in one case of Down syndrome. In general, the results of this study demonstrate the feasibility of diagnosing the major fetal chromosomopathies by culturing fetal cells taken from maternal blood. Furthermore, our initial data on the sequential sorting for fibronectin and erythropoietin receptors lead us to believe that this approach may broaden the range of fetal haematopoietic progenitors retrievable from the maternal circulation.