SINCE the discovery of kinetin by Miller et al.1 and its remarkable ability to stimulate the growth of plant tissue, much literature has accumulated on this subject and has been reviewed recently2. The effect of kinetin has been tested on micro-organisms, especially protozoa3–7. While some investigators have reported that kinetin exerted no effect on bacteria8–10, it is known to promote changes in population in some bacteria9 and to stimulate the growth of Escherichia coli7 as well as some yeasts10.