The coil-globule transition of a polystyrene chain (M-w = 113 000, M-w/M-n = 1.03) randomly labeled with a pyrene derivative was studied in cyclohexane under dilute conditions by fluorescence. The coil-globule transition temperature was found to be around 25 degreesC from the presence of a break point in the pyrene excimer-to-monomer fluorescence intensity ratio plot with temperature. Analysis of the pyrene monomer fluorescence intensity decays with the fluorescence blob model modified to consider the presence of ground-state pyrene pairs allowed for the determination of the chain radii at several temperatures between 12 and 50 degreesC and confirmed the occurrence of a coil-globule transition. Fluorescence was found to be a reliable technique for studying the coil-globule transitions in dilute solutions of low-molecular-weight polymers where stable globules exist without the interference of polymer aggregates in a large temperature interval.