This article is intended as a summary of some of the work which has been done, over the past ten years, on the biosynthesis of porphyrins. The treatment accorded to this subject should not be considered to be that of an exhaustive review article. It will consider only those papers which, in the author’s opinion, are most pertinent to the particular discussion. The article will attempt to develop and describe those experiments which have uncovered the precursors of the porphyrin molecule and those which have established the relationship of its synthesis to the other metabolic events occurring in the cell.