The isolation, crystallization, and partial identification of potato factor II, a stimulator from the chemically neutral fraction of potato extract, is described. The compound was originally found to stimulate elongation of dwarf peas grown under red light, a gibberellin bioassay. It melts between 137 degrees and 139 degrees . In paper chromatography it migrates to R(F) 0.62 in isopropyl alcohol: ammonium hydroxide: H(2)O (10:1:1, v/v). Based on infrared and NMR data, it does not contain a lactone ring and possibly possesses an amide radical and an OH(-) group, as well as many methylene radicals. Potato factor II may be similar to certain of the fatty acid derivatives previously reported to stimulate growth of excised sections, but it is unique in that it stimulates growth of intact plants. This effect points to the need for completely separating neutral from acid gibberellin-like substances when the latter are assayed on dwarf peas.