The fluorescence decay characteristics of 2-aminopurine (2AP) and 2-aminopurine riboside (2APr) have been investigated as a function of excitation and emission wavelength in aqueous and ethanolic solutions. Global analysis of the decay data shows that 2AP exists as two emitting species, whereas 2APr exists as a single species. This is attributed to 9H/7H tautomerism of 2AP. The proportion of 7H tautomer is estimated to be 20% in ethanol and 40% in water.