Normal and malignant hematopoietic cell lines, with the exception of MOLT-3, were unable to grow in the methionine-depleted medium which was supplemented with homocysteine. Normal lymphocytes were less stimulated by mitogens in the medium containing homocysteine. Colony-forming units in culture from normal bone marrow cells were not formed in the medium in which homocysteine was substituted for methionine. These data suggest that there are no differences in the methionine requirement for cell growth between normal and malignant hematopoietic cells.