We have combined in vitro clonogenic culture and a highly sensitive stain for haemoglobin to compare the influence of EPO, IL-3, SCF, TGFbeta1, MIP-1alpha and IFNgamma, to directly stimulate cells in the progenitor compartment to develop towards the erythroid lineage. Three cell lines were chosen, as they exist developmentally arrested in the progenitor compartment, yet in a pliant state of maturation. HEL (erythroleukaemia) and K562 (CML-derived) cell lines, may, under appropriate stimuli, develop erythroid characters, whilst the third, U937 (as control cell line), may be stimulated by DMSO to differentiate to myeloid cells. After in vitro semi-solid methylcellulose culture with these cytokines, resulting colonies were stained with 2,7-diaminofluorene (DAF), which sensitively stains haemoglobin blue. Haemoglobin production was low in HEL and K562 cells and absent in U937. Cytokine analysis showed varying levels of influence depending on the starting level of cell line maturation. EPO and TGFbeta1 maximally stimulated haemoglobin production in the HEL and K562 cell lines. This differential cytokine stimulation analysis combined with sensitive DAF haemoglobin detection could be applied in the study of many erythropoiesis-deficient patients or primitive erythropoiesis.