Two styrylpyrone, three terphenylquinone, and six diphenyl-substituted tetronic acid derivatives were tested for in vitro antimicrobial activity. The best inhibitory responses were seen with hispidin, bisnoryangonin, and vulpinic acid against Gram-positive organisms, including the acid-fast Mycobacterium smegmatis, and with atromentin against the acid-fast bacterium, the Gram-negative organisms, and Candida albicans. However, all of the observed activities were low relative to those normally associated with clinically useful antibiotics.