Spectral and kinetic transformation studies of gelatin films based on 4-keto wild-type bacteriorhodopsin (BR) and 4-keto D96N mutant BR were carried out using absorbance spectroscopy. Spectral heterogeneity in the 400 nm range, assumed to be associated with the M-intermediate state, previously characterized for films of 4-keto wild-type BR, was observed in the 4-keto D96N mutant BR. This heterogeneity is associated to a greater extent with chromophore replacement than with amino acid replacement. The time constants of the M-decay are larger for all kinetic components for 4-keto D96N mutant in the absence of sodium azide. In addition, the contribution of the most long-lived component of the M-state decay is almost twice as large as for the film without sodium azide as it is for a film with sodium azide. This sodium azide effect on the M-state decay kinetics is opposite to that observed in the 4-keto wild-type BR. The comparison of the kinetics and spectral transformations of both pigments suggests that films containing 4-keto D96N mutant hold greater promise as media for information storage and retrieval.