Endogenous concentrations of plant growth regulators G1, G2, G3 from leaves of French-planted Eucalyptus grandis were determined. The leaves were extracted with methanol and the resulting extracts were purified by means of silica gel column chromatography and reversed-phase medium-pressure liquid chromatography. Improved synthesis, purification and physico-chemical characterization of the G factors, for use as external standards, were developed.