OBJECTIVE To analyze the effect of conventional chemotherapy on haematopoietic progenitor cells (HPC) from peripheral blood (PB). METHODS The present work studies the behaviour of CFU-GM from PB in 47 patients subjected to conventional chemotherapy with the following diagnoses: non-Hodgkin's lymphoma (NHL): 16; Hodgkin's disease (HD): 8; multiple myeloma (MM): 5; acute leukaemia (AL): 8; solid tumor (ST): 10. A total of 57 studies was performed. As controls, 51 samples of PB from healthy subjects were used. Cultures were made in semisolid medium (methylcellulose), using PHA-LCM as stimulant, evaluating the growth of clusters (cl) and colonies (col) on days 7 and 14. RESULTS Our findings show that in the overall series of patients the number of clusters from days 7 and 14 and of colonies-7--that is the most differentiated progenitor cells--were decreased with respect to the controls while colonies-14 were slightly increased. When the patients were separated by diagnostic groups, the col-14 were found to be increased in ST (p = 0.03) and in AL; in NHL col-14 were the same as in the controls. In the patients with HD all progenitor cells, including col-14 were much lower than the control values (p = 0.005). In order to determine whether the kind or the amount of chemotherapy received might affect these progenitor cells, we have analyzed the cases of NHL, 11 patients treated with moderate chemotherapy versus 12 patients receiving intensive chemotherapy: a stronger degree of growth in the latter, although with no significant differences. On comparing the cases that had received little previous chemotherapy (< 5 courses) against those who had received more than 5 courses growth was seen to be stronger in the patients who had received the fewest courses (p = 0.04). CONCLUSIONS These results indicate that the HPC from PB are scanty in certain diseases, such as HD and that in all lymphomas the collection of these cells for transplantation purposes should be performed before they have damaged by an excessive number of chemotherapy courses.