The photogeneration of Ag particles and clusters with 350 nm photons was studied in thin films containing poly(vinyl alcohol) and poly(acrylic acid) that were crosslinked with glutaraldehyde. Product formation occurred through two consecutive processes that were linear functions of time. Kinetic determinations showed that all the processes followed rate laws that varied linearly with I-0(2) and the [Ag+] present in the films. These findings are consistent with the occurrence of biphotonic reactions in which the light excitation step is rate-determining. Two kinetically indistinguishable particle formation mechanisms are able to replicate the empirical rate law. In these mechanisms, particles form via addition of photogenerated mobile Ag atoms to either cationic or neutral metal clusters. Mechanisms based on growth of cationic metal clusters provide the most realistic representations of the processes taking place in the films, including the formation of stable Ag-3(+) clusters as byproducts of the metal crystallite generation.