Friend erythroleukemia cells in culture can be induced to differentiate along the erythroid pathway by dimethyl sulfoxide and a variety of organic polar compounds. Since this system appears to be a reasonable model to uncover agents with the potential to decrease the malignant phenotype of certain cancer cells through maturation, we have instituted a search for new and effective inducers of differentiation. To this end, we wish to report on the capacity of a series of pyridine derivatives to induce erythroid differentiation, which is monitored by the attainment of specialized function (i.e., the ability to synthesize hemoglobin detected as benzidine-stained cells). Three types of derivatives, acetamidopyridines, acetamidopyridine N-oxides, and acetamido-1-methyl-2-pyridones, were prepared and characterized. All but one of the compounds in these classes induced an accumulation of hemoglobin by Friend cells, although pyridine alone was not an effective inducer of differentiation. 2-Acetamidopyridine, 1-methyl-2-pyridone, and 1-methyl-5-acetamido-2-pyridone caused induction of maturation equivalent to dimethyl sulfoxide at concentrations approximately 100-fold lower than the polar solvent. It is interesting to note that all of the compounds tested which caused differentiation in this cell system contained the sequence -C(=O)-N(R)- (R = H or CH3) either attached to the heterocyclic ring or as part of the ring structure itself.