The statistical problem of bridging is closely associated with the problem of heterogeneity in dose-finding studies. There are some distinctive features in the case of bridging which need to be considered if efficient estimation of the maximum tolerated dose (MTD) is to be accomplished. The case of two distinct populations is considered. Extensions to several populations are, at least in principle, straightforward although, in practice, likely to be awkward and infrequently encountered. The goal is to make efficient use of information gained in one study in the context of a second study. Since working models are typically misspecified it is not possible to just add a further parameter to deal with an added source of variability.