The photodynamic effect of the arginine hematoporphyrin derivative (HpD-Arg 2 ) on the growth of selected Pseudomonas aeruginosa clinical isolates is described as compared to the effect of hematoporphyrin derivative (HpD). Growth inhibition of HpD-Arg 2 of three Gram-positive strains (Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus) and five laboratory strains of Gram-negative bacteria (Escherichia coli, Proteus vulgaris, P. Aeruginosa, Klebsiella pneumoniae and Enterobacter cloacae) was observed as well. Serratia marcescens strain was resistant to light-activated HpD-Arg 2 or HpD. The antimicrobial activity of light-activated HpD-Arg 2 against P. aeruginosa may offer an additional option in the anti-pseudomonal therapy of wounds.