Fast transient fluorescence technique (FTRT) was used to measure pyrene (4) Lifetimes during dissolution of glassy polymer, which is formed by free radical polymerization of methyl methacrylate (MMA), and Py was introduced during polymerization as a fluorescence probe to monitor swelling and dissolution. The dissolution process of poly(methyl methacrylate) (PMMA) glass was performed in chloroform (80%)-heptane (20%) mixture. Fluorescence lifetimes of Py from its decay traces were used to monitor the dissolution process. A model was derived for low quenching efficiencies for measuring mean lifetimes, [tau], of Py and it was observed that [tau] values decreased as the dissolution process proceeded. Desorption, D and mutual diffusion, D-m coefficients of Py molecules were measured during dissolution of PMMA and found to be around 1.19 x 10(-6) and 1.23 x 10(-6) cm(2) s(-1), respectively.