The influence of various tetracycline hydrochlorides (TC HC concentrations: 3,6,8 and 12 × 10^–3g 1^–1), on growth and protection against bacterial infections in submerged Pleurotus saca cultivation was studied. 8 × 10^–g 1^–1 of TC HC added before the inoculation showed a reasonable protection effect, simultaneously promoting the growth of fungus. In the presence of tetracycline the lag phase was prolonged, and the final biomass production increased by 200 % on average. If the infection occurred during the cultivation process, even 12–16 × 10^–3g 1^–1 of added TC HC, could not prevent bacterial infection.