The population of Datura stramonium L. var. tatula Torr and Datura wrightii Regel was heterogenous in the numerical and structural composition of karyotypes. Datura wrightii Regel contained, as well as aneuploid sets, a 35% karyotype with a diploid set of chromosomes (2n = 24); there were no chromosomes with satellites and there were 1-2 microchromosomes in 29.6% of the metaphases. Datura stramonium L. var. tatula Torr included biotypes with a chromosome number of 21-25; in 88.5% of the metaphases there were chromosomes with satellites and 60% of the metaphases contained 1-3 microchromosomes. According to the content of the main alkaloids Datura stramonium L. var. tatula Torr can be considered a predominantly hyoscyamine type, Datura wrightii Regel also containing scopolamine.