In induced autotetraploid forms of Datura stramonium and Hyoscyamus niger was observed considerably lower pollen fertility and seed formation than in initial diploid forms. Germination capacity was slightly decreased, from 40.5% for diploid to 38.5% for tetraploid seeds of D. stramonium and from 73.5% for diploid to 71% for tetraploid seeds of H. niger. The seeds of tetraploid forms had longer germination period, germinated and reached germination maximum later. The reproductive ability was sufficient for successful propagation of tetraploid forms in both species.