The rose Bengal photosensitized oxidation of the (+) and (−) stereoisomers of α-pinene, β-pinene and limonene has been optimized to produce sufficient quantities of hydroperoxides for antimicrobial screening. Experimental conditions allowed the production of highly concentrated solutions of hydroperoxides (approximately 2 M, approximately 30 w%). The antimicrobial activity of each hydroperoxide solution was evaluated by measuring their minimum inhibitory concentration (MIC) (1,2). All the hydroperoxides behave as powerful antimicrobial agents (similar to hydrogen peroxide). The MIC values were almost independent of the nature of the parent terpene but depended of the nature of the bacterial colony (five conventional families, met in human pathologies, were tested).