We have studied the effect of disorder on the radiative properties of semiconductor quantum wires by time-resolved photoluminescence spectroscopy. The dependence of the radiative lifetimes is measured over a temperature range extending from 8 to 150 K. At low temperatures we find that the measured dependence does not conform to the theoretical prediction for recombination of free excitons in a quasi-one-dimensional system due to the major influence of disorder. An extension of the theory is developed in order to take into account exciton ionization and the contribution of free carriers. A mean localization length for excitons is also estimated from the radiative lifetime at 8 K. [S0163-1829(99)12903-5].