Several investigations have been concerned with amino acids as sources of nitrogen for the production of penicillin. Foster et al. (1943) were apparently the first to test individual amino acids as sole sources of nitrogen for penicillin production by Penicillium notaturn in surface cultures, finding that nitrate nitrogen was superior to amino acids. In subsequent experiments with submerged cultures, these workers (1946) noted that glutamic acid was superior to asparagine or glycine as a nitrogen source for one mold strain tested. With another strain, however, various single amino acids did not promote penicillin formation in the basal medium, either with or without additional sources of nitrogen. Large increases in penicillin yield obtained in media containing corn steep liquor were found by White et al. (1945) to be at least partially due to arginine, histidine and glutamic acid. When a mixture of these compounds, in concentrations of 30 mg., 30 mg., and 400 mg. per 100 ml., respectively, was added to a basal medium containing glucose, lactose and mineral salts, yields assaying 80-90 per cent of that obtained in corn steep media resulted. This finding suggested that amino acids might be involved in the biosynthesis of penicillin: would appear that in some way this mold is perhaps able to convert one or several of the amino acids to a part of the penicillin molecule through its metabolic processes. It was further shown that hydrolyzed corn steep liquor is unsatisfactory for penicillin production, in comparison with hydrolyzed proteinfree liquor, the large increase in free amino acids resulting in conditions unfavorable for penicillin formation. Halpern et al. (1945) reported increased penicillin production upon the addition of proline or glutamic acid to synthetic media. Aspartic acid could be substituted for glutamic acid, and the addition of arginine also had a slight stimulatory effect. A number of