A new method of gibberellin A3 detection based on high-performance liquid chromatography has been elaborated. It combines high accuracy and low cost, and includes the following stages: fixation with liquid nitrogen; extraction of alcohol-soluble substances; purification with freezing, reextraction in ethyl acetate, and thin-layer chromatography; and detection with HPLC. Chromatographic conditions and methods of substance identification have been determined. The method allows the use of modest amounts of plant material (5–20 g), at which variability does not exceed 7%, and the total loss of substance is approximately 3%. The results of gibberellin A3 detection in buckwheat are presented.