The use of ionising radiation for sterilisation of drugs is now a well-established technology. In this paper, we have studied the stability of orciprenaline and fenoterol, two sympathomimetics, after gamma irradiation. High performance liquid chromatography (HPLC) chromatograms indicate that a dose of 25 kGy or lower slightly affects the amount of impurities. Gamma irradiation produces free radicals which appear relatively stable; these radicals could be detected even after a storage period of more than 12 months. The increase of free radicals versus dose was performed using polynomial regression analysis. Electron spin resonance (ESR) measurements could be used for the evaluation of the irradiation dose.