Photo-oxidation of some representative spiropyrans and spiro-oxazines does not seem to involve singlet oxygen O-2((1) Delta g). The photochromes rather behave, in the spiro and merocyanine form, as O-2((1) Delta g) quenchers. Only a methoxy-nitro benzopyran derivative was found to promote formation of singlet oxygen. Superoxide anion O-2(radical anion) is likely the activated oxygen species responsible for their oxidative photodegradation.