[en] Genetic system of ''waxy locus mutation'' in barley pollen grains was used to estimate mutagenic activity of low background ß-irradiation (about 2.5 mR/h), uranium natural isotopes being used as irradiation source. In 3 out of 4 experiments age frequencies of waxy mutations were observed in irradiated plants. But the noted increase mainly had a tendency character and was statistically trustworthy only in one experiment