The relation between the lifetimes of the triplet states of various porphyrins and their photosensitizing effects on the photodynamic therapy (PDT) of tumor has been examined. Ga-DP, Zn-DP, Mn-DP and P-II are used as the photosensitizer. The triplet lifetimes are obtained to be 57 ms (Ga-DP), 26ms (Zn-DP), <10 us (Mn-DP) and 9 ms (PII). The phosphorescence of Ga-DP in tumor-bearing golden hamsters are measured both in tumor tissue and in liver. They show bi-expo-nential decay with the lifetimes of about 5 and 20ms. The PDT effects have been quantitatively investigated for in vitro experiments; upon irradiation the growth inhibitions of mouse p388 leukemia cells are obtained as a function of concentration of Ga-DP, Zn-DP, Mn-DP and PIT. The experimental results indicate that the PDT effects depend essentially on the triplet lifetimes of the photosensitizers.
