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Interaction of photosensitizer, chemotherapeutic drug and HSA: Implications for photosensitized tumour therapy G.Streckyte, S.Bagdonas and R.Rotomskis Photosensitized tumour therapy (PTT) used in combination with antitumour drugs leads to enhanced tumour and tumour cell response [1,2]. It was demonstrated that combination of PTT with drug Adriamycin (ADM) increased tumour destruction [1,3]. The results obtained in experiments in vitro and in vivo show that synergistic effect depends on the sequence of the combination of PTT with chemotherapeutic drug [1,4]. Although not a few papers about the results of combined treatment were published in the recent years, so far no reports appeared on the primary photoprocesses in the aqueous mixture of photosensitizer and chemotherapeutic drug. Interaction of the drug with photosensitizer may alter absorption properties of sensitizer in the red spectral region, which is important for clinical treatment. It may also have impact on phototransformation rate of sensitizer. Changes in sensitizers absorption induced by the complexation with chemotherapeutic drug may also have consequences for the evaluation of photodynamic dose. Our aim was to study primary events in the aqueous mixtures of photosensitizer and antitumour drug. The spectra of PH - ADM complex alone and in the presence of human serum albumin (HSA) were examined in order to detect the influence of interaction on the absorption properties of sensitizer. The influence of interaction on the photomodification of PH was also investigated.