Using laboratory water-tank experiments, detrainment from a vertical jet rising through a density interface is explored. The experiments reveal that detrainment only occurs for a specific range of two governing parameters, the Richardson number associated with the vortices and the normalized interface height. The shape of the detrainment domain is explained with simple physical arguments involving velocity gradients, baroclinic torques between the pure unmixed fluid and the environment, and baroclinic torques between the mixed fluid and the surrounding fluid. Detrainment is only observed when the penetrating jet consists of fluid with two different densities. ¿ 1997 American Geophysical Union