The in vitro effect of increasing concentrations of retinoic acid on the growth of day 7 and day 14 CFU-GM and of pre-CFU-GM from patients with myelodysplastic syndromes has been studied. Unlike in normal cells, where retinoic acid enhances the in vitro growth of myeloid progenitors, there was an overall inhibition of bone marrow progenitors from patients with myelodysplastic syndromes at concentrations of 10(-7) to 10(-6) M retinoic acid, with the exception of day 14 CFU-GM whose growth may be enhanced by 10(-7) M retinoic acid.