Hematoporphyrin (Hp) solutions were subjected to a wide range high intensity (0.2-10.0 GW/cm2) near-UV laser pulse radiation (lambda exc = 355 nm, pulse duration 30 ps). The formation of stable Hp photoproducts was followed by UV-VIS absorption spectroscopy and liquid-gel column chromatography. As judged by the influence of free radial scavengers, a significant part of the products is assigned to arise from the reaction of Hp with OH.(and H.) radicals. Using nitroxide radicals (TEMPO and TEMPONE) and the spin trap DMPO the generation of primary transient photoproducts, hydrated electrons (eaq-), OH. and H. radicals, was studied varying the pulse intensity at a constant absorbed light energy. The results showed that bi-photonic processes are responsible for the observed product generation (different for eaq- photoejection and OH.(H.) formation). A tentative diagram of the Hp excitation routes involved in the present high intensity laser flash photolysis is suggested. According to it, OH. and H. radicals are supposed to be generated in a resonance energy transfer reaction from highly excited Hp** to water molecules (H2O sensitization).