The purpose of this project is to examine the metabolism of amino acids, particularly proline, by anaerobic organisms found in dental plaque. By means of both batch culture of saliva technique and an anaerobic enrichment chemostat procedure approximately one dozen isolates have been obtained, presumptivley identified as Peptostreptococcus anaerobius, capable of the reduction of proline to Delta-NH2 valeric acid. the utilization of different substrates by these organisms and a stock ATCC strain of P. anaerobius (27337) has been examined in washed cell suspensions. In preliminary experiments the stock ATCC strain has been shown to use proline as an electron sink for the oxidation of alanine, pyruvate and glucose. Similar activity was found for leucine and glycine. The presence of glucose in the growth medium markedly reduced the ability of the cells to utilize amino acids.