[en] The purpose of these experiments is to explore the mutagenesis rhythm and breed high productive strains of actinomycete '5406'. The single colony agar pieces of strain F₃₅₈ were treated with fast neutron and ⁶⁰Co-γ ray irradiation Two mutants have been selected from 20025 treated single colonies. The output of cytokinins from them is higher than from strain F₃₅₈. The original strain 'Mu-Tan-al' rejuvenated by freezing was treated with several physical and chemical mutagens. The mutagenesis rhythm has been summed up tentatively. Eight mutants obtained from 93014 treated single colonies produced more '5406' antibiotics than that of strain 'Mu-Tan-al,. The effect of mutant 'N2-10-Ra3' was the best