Linsmaier and Skoog have made a systematic study of the organic -requirements of Tobacco cultures in addition to the studies of mineral requirements done by Murashige and Skoog. It was found that of all MS vitamins only Thiamine and Inositol are essential. The optimum -concen-tration for Thiamine HCl was 0.4 mg/l (MS 0.1 mg/l). At a lower concentration growth decreased and the cells became necrotic after 4 weeks. Inositol also had a very stimulatory effect on the cell growth but was not as essential as Thiamine. All other Murashige & Skoog vitamins were not required for cell growth and could be ommitted without any disadventageous effect. Folic acid, p-Aminobenzoic acid, l-Glutamic acid and Ascorbic acid also had a positive influence on cell growth of Nicotiana tabaccum, however the effect was much less than that of Thiamine and Inositol