Cells of the human myeloid leukaemia cell line ML-1 were exposed to differentiation inducing doses of dimethylsulfoxide (DMSO) and retinoic acid (RA). DMSO (but not RA) caused an inhibition of cell growth which was reversible. Some granulocytic maturation associated changes were induced by both agents: nuclear segmentation in 10-20% of cells, B43.4 antigen positivity. In contrast, several other markers were not induced: nucleoli persisted in almost 100% cells including the segmented ones, the nuclear membrane regions did not stain with Victoria blue B (which stains these regions in normal neutrophils), the expression of other antigens of mature neutrophils was also not induced. Maturation asynchrony and non-physiological segmentation of round and oval nuclei were observed. Examination of nucleoli on a single cell level revealed a reversible decrease of pre-rRNA synthesis in 28-48% of the induced cells. These results indicate that terminal differentiation did not occur and confirm the dissociation in induction of various differentiation markers.