Hematoporphyrin monomethyl ether (PsD-044) is a new promising tumor-photolocalizing and photochemotherapeutic agent, and its distribution in different tissues of S180 sarcoma-bearing mice was determined by fluorspectrophotonietry. The peak values of drug concentration in diffrent tissues ap- peared at 30 min after i.v. administration of 20 mg/kg of PsD-044. The maximum values of tumor to muscle and tumor to skin ratios were 12. 2 and 3 respectively, which was achieved at 3 h post drug injection. Drug concentrations in different tissues at this time were in order of liver>tumor>lung>skin> kidney>spleen(?)heart(?)muscle.The pharmacokinetics of PsD-044 in mice was fitted by an open three compartment model. The pharmacokinetic parameters calculated were shown to be essentially consistent with the determination of tissue distribution. It was also shown that PsD-044 can't pass through blood-brain barrier.