The photoreaction of caffeine with dioxane, tetrahydrofuran, tetrahydropyran, anisole, and ethyl ether has been studied. Ultraviolet irradiation of aqueous solutions of caffeine and cyclic ethers in the presence of benzophenone or acetophenone using a pyrex filter yields substitution products. Substitution occurs at the 8-position of caffeine. The photoreaction of caffeine with ethyl ether gives 8-(1-ethoxyethyl)-caffeine and 8-ethylcaffeine while in the presence of anisole caffeine has been found to be completely inert. The structures were determined by infrared, nuclear magnetic resonance, and mass spectrometry.