A vast storehouse of genetic variability is contained in collections of Nicotiana tabacum and Nicotiana species. Methods and techniques of using this material to alter chemical constituents of commercial tobacco are discussed. Simple Mendelian procedures that have resulted in improved varieties may also be used to change chemical constituents. Male-sterility permits the rapid production of F1 hybrids in special situations. Interspecific hybridization allows the transfer of new germplasm. The haploid/diploid method offers instantaneous homozygosity when a haploid is doubled. Any diploidized haploid that shows a favourable change in a chemical trait automatically represents a potentially useful breeding line. Parasexual hybridization is a new technique that involves the fusion of protoplasts. Fusion of protoplasts between diploid tobacco and a species, that cannot be crossed with it by conventional means, provides a valuable new allopolyploid. Thus, conventional breeding methods aided by these new adjunct techniques provide the basis for favourably altering chemical constituents in the leaf and smoke.