Films of zinc porphyrins in polyvinylpyrrolidone have been formed and studied by spectrophotometric methods. Diffusion of gaseous pyridine through a film of polyvinylpyrrolidone containing zinc tetraphenylporphyrin leads to a rearrangement of the porphyrin dye with the formation of aggregates. Absorption and fluorescence spectra are complemented by observations under an inverted Nikkon microscope equipped for epifluorescence, using st Titane-Sapphire Laser as the excitation source. Fluorescence is collected through an optical fiber. The technique allows for the study of well-defined zones in the film.