The inheritance of resistance to black root rot in tobacco, caused by the fungus Thielaviopsis basicola (Bek. and Br.) Ferr., was studied with a view of developing higher resistance by combining genes from various sources. The studies were conducted under greenhouse conditions during the winter and summer seasons of 1951-52. The five parental lines, the F₁ hybrids between them and five of the F₂ populations were included in the winter study when the temperature averaged between 65° and 70° F. The five parental varieties, all of F₁, F₂, and the backcross populations were included in the summer study when the temperature could not be controlled in the greenhouse. The evaluation of resistance was done on the basis of visible damage to the roots of the seedling plants. / M.S.