The fluorescence lifetime (tau (f)) of trans-stilbene has been evaluated in zeolites Y and ZSM-5 under various conditions, e.g., at low temperature and in the presence of coadsorbed solvents. To make these measurements, an indirect method was developed to measure short-lived (<100 ps) fluorescence lifetimes with a single laser pulse. In dehydrated NaY, (f,TS) was 52 ps compared to 66 ps in hexane and 32 ps in methanol. When the NaY sample was subsequently bathed in either water or cyclohexane, tau (f,TS) increased by a factor of 4 and 5, respectively, reflecting decreased mobility of trans-stilbene because of blocking effects of the solvent. However, with small amounts of coadsorbed water equivalent to 13 H2O/supercage, tau (f,TS) decreased by a factor of 2, reflecting increased mobility of trans-stilbene. Small amounts of coadsorbed cyclohexane only increased Z(f,TS) Values of tau (f,TS) in the solvent-free zeolites were significantly smaller (higher degree of probe mobility) than those published a decade ago and contradicted the earlier conclusions regarding the mobility of stilbene in zeolites. The possible reasons for this are discussed.