1. 1. Bacteria isolated from soil which can utilize the tobacco alkaloids as sole sources of both nitrogen and carbon are classified into two types, A and B, of which type A bacteria are capable only to break down nicotine; whereas B decomposes nornicotine and anabasine as well as nicotine. The degradation course of nicotine by both types is the same and represented as follows: nicotine → pseudoöxynicotine → γ-keto-γ-(3-pyridyl) butyric acid → 3-succinoyl-6-hydroxypyridine → aliphatic compounds. 2. 2. Nornicotine is transformed by the bacteria, type B, along the following scheme: nornicotine → 6-hydroxymyosmine → 3-succinoyl-6-hydroxypyridine → aliphatic compounds. Anabasine is degraded by the same bacteria along the pathway: anabasine → 1′,6′-dehydro-6-hydroxyanabasine → 3-glutaroyl-6-hydroxypyridine → aliphatic compounds. 3. 3. The essential action of the bacteria of both types on the tobacco alkaloids consists of dehydrogenations and hydroxylations. The sequence of these steps is the reverse in nicotine oxidation as compared with the oxidation of nornicotine and anabasine. 4. 4. Oxygen uptake of the tobacco alkaloids and of related compounds in the presence of bacteria has been observed. 5. 5. A modified method is described for the preparation of 6- and 2-hydroxynicotine and of dihydrometanicotine. 6. 6. Nicotyrine, 3-pyridyl methyl ketone, 3-pyridyl n-propyl ketone, and oxynicotine can not be intermediates of the nicotine degradation by the bacteria. Nicotinic acid seems not to be an intermediate in the nicotine degradation, but the acid can serve as sole source of nitrogen and carbon for both types of bacteria, and is degraded through 6-hydroxy nicotinic acid.