In order to improve certain agricultural and technological properties of tobacco cultivars, attempts were made in Poland at inducing mutation by means of ionizing radiation. Germinated seeds of four Nicotiana tabacum varieties and one Nicotiana rustica variety were exposed to gamma radiation. The seeds were irradiated with two doses of gamma rays, i.e. 18 000 R for four minutes 17 seconds and 25 000 R for five minutes 57 seconds.