Intermolecular hydrogen abstraction by benzophenone in a poly(methyl methacrylate) host is studied by using the new technique of holographic photochemistry. In this technique the temporal course of a photochemical reaction is followed by following the growth of a hologram resulting from the photochemistry. The photochemistry is found to involve two steps, each involving the absorption of two laser photons. In the first step a benzophenone triplet state abstracts a hydrogen atom from the host to produce a ketyl radical. This ketyl radical reacts with the host, producing a long-lived intermediate that is involved in the second step. The hydrogen abstraction reaction is found to occur only from a higher nπ* triplet state. No irreversible hydrogen abstraction occurs from the lowest nπ* or ππ* triplet state. © 1981 American Chemical Society.