The effect of pre-sowing seed treatment with immunostimulant Bisol-2, red light and low frequency electromagnetic field on the content of fungitoxic substances of phenolic nature – phytoalexins (isohemigossypol and gossypol-equivalent) in infected etiolated cotton seedlings of S-4727 cultivar infected with Verticillium wilt pathogen was studied. It was found that photostimulation of seeds by red light induces phytoalexin formation in cotton tissues infected by the pathogen 1.5–2 times more effectively in comparison with Bisol-2 preparation or inducer of electromagnetic nature. The correlation between the content of phytoalexins in the tissues of seedlings, parameters of induction curves of chlorophyll fluorescence and the number of plants with signs of wilt lesions grown from treated and untreated seeds with inducers was revealed. This indicates the possibility of using red light and weak low-frequency electromagnetic fields as factors contributing to the intensification of phytoalexin formation in response to Verticillium wilt infection of cotton.