The effects of benzoquinone, naphthaquinone and anthraquinone on the growth of tomato callus, whole plants of tomato and on rooting of mungbean cuttings were studied. Naphthaquinone effects on some oxidases and on the isozyme patterns of peroxidases in all the three systems were also observed. Quinones increased callus growth, the number of roots initiated in mungbean cuttings and the growth of tomato plants, significant increases being obtained with 10-s M naphthaquinone. Naththaquinone also decreased the activities of IAA oxidase, ascorbic acid oxidase and polyphenol oxidase, and led to the disappearance of one of the isozyme of peroxidase in all systems.