Diazosulfonates decompose in water upon UV irradiation, forming diazonium salts as intermediates. Therefore, these compounds can be considered as diazonium ion sources, which are thermally very stable, easy to handle, and suitable for longtime storage. Several low-molar-mass diazosulfonates have been used in UV initiated azo coupling reactions with a large variety of phenols, naturally occurring substances, and drugs and the results were compared to those obtained with free diazonium ions. The conditions for a successful coupling reaction and the UV absorptions of the products were studied in detail. The concept could be transferred to polymers containing diazosulfonate functional groups. A preliminary application test proved the suitability of these polymers as analytical reagents in quick assays.