The time-resolved, fast transient fluorescence technique, which uses a strobe master system, was employed for studying the swelling of a disc-shaped poly(methyl methacrylate) gel. The disc-shaped gel was prepared by free-radical copolymerization of methyl methacrylate and ethylene glycol dimethacrylate. Pyrene (Py) was introduced as a fluorescence probe during polymerization. After this gel was dried, swelling and slow-release experiments were performed in chloroform at room temperature. Lifetimes of Py were measured during in situ swelling and slow-release experiments. An equation was derived for low-quenching efficiencies to interpret the behavior of lifetimes in and out of the gel during swelling. Py lifetimes in the gel decreased as swelling proceeded, but Py lifetimes out of the gel stayed constant during the slow-release experiments. The Li-Tanaka equation was used to determine the cooperative and mutual diffusion coefficients, which were around 10(-5) and 10(-7) cm(2)s(-1), respectively. (C) 2000 John Wiley & Sons, Inc.