Results are presented from a series of laboratory experiments in which the interaction of a turbulent buoyant jet with a localised patch of grid-generated turbulence has been investigated. The experiments show that the effect of the turbulent patch is to arrest the structural development of the buoyant jet at a location determined by the relative values of the r.m.s. turbulent velocities in the patch and jet, respectively. Measurements of the breakdown distance z(c) from the jet source have been compared successfully with the predictions of a scaling analysis for the limiting cases of momentum- and buoyancy-dominated regions of the buoyant jet. (c) 2006 The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.