For at least 35 years, five major plant-growth regulators have predominated the field of plant growth and development. One of the reasons for the preoccupation with indole-3-acetic acid, the gibberellins (especially GA 3 ), abscisic acid, the cytokinins, and ethylene has been the relatively large quantities with which these metabolites can be obtained from either natural sources or by synthesis. The bulk of the literature attests to the availability of these compounds. For example, the literature concerning gibberellins had already amounted to 632 abstracts and articles by 1957 66 when gibberellin, specifically GA 3 , was a relatively newly discovered compound compared to indole-3-acetic acid and ethylene.It is significant that the five major plant-growth regulators have, at last, all been found in microorganisms. Indole-3-acetic acid was discovered in Rhkopus suinis n early in the developmental history of plant-growth regulators and was called rhizopin. Gibberellins were isolated from Gibberella fujikuori (Fusarium moniliforme). 5 Ethylene has been found emanating from numerous fungi. 30 Abscisic acid and its metabolites have been recent topics of discussion relative to their identification and large titer in Cercospora cruenta.' 9 "-54 This organism produces mostly 2-cis-( + )-abscisic acid, which is the active isomer, as opposed to 2-trans-{ -)-abscisic acid which is inactive. The last well-known metabolites to be isolated from microorganisms, the cytokinins, have only recently been reported. These include transzeatin, franj-zeatin riboside, and the novel cytokinin 6-(4-hydroxy-l,3-dimethyIbut-frarc.y-2-enyIamino)-9-B-D-ribofuranosylpurine 6lf from Pseudomonas syringae pv. savastanoi, the causal organism of olive knot, which includes stem galls in ash, oleander, privet, and jasmine. Initial studies with crude ethyl acetate extracts of the culture filtrate showed that olive and tobacco callus cultures were stimulated and this indicated the probable presence of a cytokinin. Thus, all of the "major" classes of plant-growth regulators have been accounted for in microorganisms. Furthermore, it appears that the genetic influence governing the production of these important compounds has not been deleted during the evolutionary process. Until recently, it was believed that these compounds were almost totally responsible for events taking place in the differentiation and development of plants including, in certain cases, the etiology of plant diseases.Any discussion of plant-growth regulators that includes compounds other than these five often raises a hue and cry among certain circles of scientists. But the evidence supports the facts to show that there are fungal and bacterial metabolites that promote plant growth and others that inhibit it. Earlier, we reviewed the literature on (+ )-hexylitaconic acid, from Aspergillus niger K-88, that promoted lettuce root growth by approximately 250%, relative