Robert S.Maier and Daniel L.Stein University of Arizona The Effect of Focusing and Caustics on Exit Phenomena in Systems Lacking Detailed Balance (672K, PostScript, 11 pages) ABSTRACT. We study the trajectories followed by a particle subjected to weak noise when escaping from the domain of attraction of a stable fixed point. If detailed balance is absent, a _focus_ may occur along the most probable exit path, leading to a breakdown of symmetry (if present). The exit trajectory bifurcates, and the exit location distribution may become `skewed' (non-Gaussian). The weak-noise asymptotics of the mean escape time are strongly affected. Our methods extend to the study of skewed exit location distributions in stochastic models without symmetry.