Effects MTH on growth of erythroid and myeloid cultures. Mononuclear cells derived from normal bone marrow were cultured in semisolid medium in the presence of the indicated concentrations of HU (μM) (A) or MTH (nM) (B). The medium contained either 1 U/mL EPO for development of erythroid colonies (○) or 10% (vol/vol) 5637 cell–conditioned medium for development of myeloid colonies (▪). Colonies of 50 or more cells were counted after 14 days of incubation under an inverted microscope. The results represent the number of colonies per plate (average ± SD of 3 independent experiments).