Beta-lactamase production in Enterobacter cloacae ATCC.13047 was enhanced by glycine, and the degree of enhancement was dependent on the concentration of glycine and the medium used. Maximum enhancement occurred with a concentration of 0.05 moles/l of glycine, and of 4 media examined enhancement was greatest on Isosensitest Agar. Enhanced beta-lactamase production evoked by glycine was compared with that following induction by various concentrations of cefoxitin. The amount of beta-lactamase produced under conditions of maximum glycine enhancement was higher than that produced by cultures fully induced by cefoxitin. Other differences in the characteristics of the enhancement of beta-lactamase production by glycine and beta-lactamase induced by cefoxitin suggested that the mechanisms of the 2 phenomena were different. The significance of this finding in terms of the interpretation of in vitro antimicrobial sensitivity tests with beta-lactam antibiotics is discussed.