Some of the general concepts which have emerged in the elucidation of the biochemical reactions and transformations which occur in living organisms, summarized very briefly, are that the basic chemical reactions in the cell are rather simple, that the celt synthesizes its complex molecules from relatively simple and available substances and that there is a biochemical unity in living matter. The picture that has emerged in studies on the biosynthesis of porphyrins and related compounds is rather a good illustration of these basic concepts. The studies have revealed that the synthesis of this "large" molecule is synthesized from two simple, readily available and ubiquitous compounds, glycine and succinic acid by relatively simple reactions. Furthermore it appears that all porphyrins and related compounds such as chlorophyll, vitamin B,= etc. in different types of cells are synthesized by the same pathway. The different porphyrin or porphyrinlike compounds merely arise by modifications occurring in the side chains in the fl-positions of the pyrrole units and by the change of the oxidation state of the heterocyclic five-membered rings contained in the structure. It is worth noting that if porphyrins were formed in prebiotic times then the enzymic steps outlined below in all probability mimic those which occurred in this early time. This conjecture seems quite reasonable for one can readily form intermediates from succinate and glycine under conditions which simulate a physiological environment and by rather simple and analogous activation steps. Furthermore these intermediates can readily be converted into porphyrins containing the biological functional isomeric structure. Besides pointing out the ease of synthesis of porphyrins it is of interest to note that porphyrins are very stable molecules for they are found in fossilized excrements of crocodile and mineral hydrocarbon oils contain porphyrins presumably of both plant and animal origin.