Ariel and Umbriel have passed through the 5:3 mean-motion commensurability if the specific dissipation function ( Q) for Uranus is less than about 100,000. There is a significant chaotic zone associated with this resonance. Due to the presence of this chaotic zone, the standard theory describing passage through orbital resonances is not applicable. In particular, there are significant changes in the mechanism for and probability of capture into resonance. Tidal evolution within the chaotic zone may have driven orbital eccentricities to relatively high values, with some probability of escape from resonance remaining. In the planar approximation, eccentricities high enough to have a significant effect on the thermal history of Ariel have not been found.