Is the objective of the invention to develop a process for the production of tagged gibberellin-(7)-aldehydes which is of general applicability. As per the invention a gibberellin-(7)-aldehyde is converted into the gibberellin-(7)-aldehyde tagged at the C-15 position of the basic gibberellin skeleton under the influences of ultraviolet radiation, in given cases after the isolation of a developing 7-Hydroxy-7,15-cyclo butane derivative, and in the presence of compounds with tritium or deuterium donor properties respectively. The process is of particular suitability for the tagging of alkali-sensitive gibberellin-(7)-aldehydes. The tagged gibberellin-(7)-aldehydes produced by the process as per invention, are of importance for instance as primary materials for the obtaining of tagged natural gibberellins and their derivatives.