The theoretical benefits of selection of mutant cell lines, for contributing improved germplasm to breeding programmes, has led to a very strong emphasis on these applied objectives, while the use of such lines for fundamental investigations has generated relatively little attention. This is particularly true in the case of cell lines modified in their response to environmental stresses. Taking as an example salt tolerance, probably the most widely studied phenotype in vitro, the strategy adopted for selection in most recent reports differs little from that used to obtain the first lines many years ago (Dix and Street, 1975; Nabors etal., 1975). It is simply being applied to an ever increasing range of species. In most cases, characterization of the tolerant phenotype is at best superficial, and sometimes non-existent. Fortunately there are sufficient exceptions to indicate the potential of basic studies on tolerant cell lines, and plants recovered from them, for providing insights into mechanisms of salt tolerance.