1. Eight introgressed lines where loci from five related and unrelated species were introduced into tabacum chromosomes were investigated. The primary purpose was to determine whether chromosome exchange regularly involved the tabacum chromosome known to bear the recessive locus corresponding to the one introduced, using selected monosomic types.
2. Introgressed loci from related species, sylvestris and setchellii were identified with the homologous chromosome in the former and with a non-homologue in the latter.
3. Results were inconsistent where N. glutinosa was the donor species. In one instance the exchange involved the tomentosa chromosome bearing the corresponding recessive. The haplo-F(co) population gave evidence that some chromosome other than the F- had received the Co segment. This might have been expected in view of the small amount of homology between glutinosa and tabacum chromosomes.
4. The situation, where even less closely related species were employed, is considered briefly.

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