Studies of the luminescence of Bacillus thuringiensis spores and DNA of chicken‐blood erythrocytes are presented. Luminescence was excited by pulse-periodic ultraviolet laser radiation with duration of a separate pulse of 20 ns. The decay kinetics of luminescence and changes in the shape of the luminescence spectrum are considered. Noticeable changes in the photoluminescence spectra with delay in the registration system are detected. For a pulse‐periodic mode of excitation, exciton–exciton quenching of luminescence in bacterial and DNA suspensions is observed. Studies of the influence of the geometrical shape of the cell on the photoluminescence spectra are performed.