Abstract: A method for measuring the release of 4-(3?-chloro-4?-fluoroanilino)-7-methoxy-6-(3-morpholinopropoxy)quinazoline or a pharmaceutically-acceptable salt thereof (the Agent) from a pharmaceutical composition, which method comprises: (i) immersing a pharmaceutical composition containing the Agent in a dissolution medium, wherein the dissolution medium comprises water and a non-ionic surfactant; and (ii) determining the concentration of the Agent in the dissolution medium at one or more time points following immersion of the pharmaceutical composition. The method is suitable for monitoring batch-to-batch variability as part of a quality control procedure; or as a means for determining the bioequivalence of different formulations containing the Agent.