The photosensitive activity of haematoporphyrin (HP) and proflavine (PF) on some biological parameters of Salmonella dublin cells was assessed. The investigations showed a decreased respiratory activity of photosensitized PF bacterial cells, accompanied by lower virulence. HP-treatment and light irradiation of salmonellae did not influence their survival in vitro, which was in contrast to the PF-incubated and irradiated cells. Light irradiation of HP- and PF-treated bacteria did not change their phagocytosis from guinea pig alveolar macrophages. In the presence of visible light the PF-treatment considerably reduced the survival rate and multiplication in alveolar macrophages in comparison with HP-treated and light-exposed bacteria. Correlation was established between the degree of structural damage, as observed by electron microscopy and the level of diminution of the chosen biological parameters, which were more strongly expressed after PF-treatment. PF as a photosensitizer which influences the bacterial genomes and its possible practical use, is discussed.