The results of "in vitro" culture of granulomonocytic precursor cells (CFU-GM) of the bone marrow from 44 patients were analysed in the present work. The correlation with the patient's haematological characteristics, their FAB subtypes (i.e., 6 cases of refractory anaemia (RA), 11 of acquired sideroblastic anaemia (ASA), 15 cases of refractory anaemia with excess blasts (RAEB), 5 cases of RAEB in transformation (RAEBT) and 7 cases of chronic myelomonocytic leukaemia (CMML), and the survival were examined as well. The technique used for cell culture was that of Pike and Robinson, following the classification proposed by Florensa for estimating the growth patterns. Anomalies of the myeloid clonal proliferation were found in 81% of the cases. There was direct correlation between the number of aggregates and the polymorphonuclear cell count, whereas the highest number of blast cells coincided with increased number of clusters in cultures. CNNL showed the highest aggregate counts. The B growth pattern (both colony and aggregate growth) was most frequently seen in CMML; pattern C2 (decreased colonies with increased aggregate count) appeared in RAEB, RAEBT and CMML, and pattern C3 (decrease of both colony and aggregate counts) was found only in RA and ASA. None of the culture findings appreciably associated with the survival.