[en] Content of polonium 210 was studied in the leaves of six varieties of Bulgarian oriental tobacco according to their class. Tobacco that had to be examined was kept for more than three years for equilibrium between polonium 210 and lead 210 to be reached. Tobacco leaves of higher classes contained smaller quantities polonium 210 compared with those of lower classes (III-V classes). This is due to leaves of the upper and middle parts of the plant with a shorter vegetation period belonging to higher tobacco classes; radionuclide penetration by the root. The established divergence from this relationship was due to some other reasons such as mechanical damage, etc. (A.B.)