Abstract:To determine the therapeutic effect of photodynamic therapy (PDT) using a new photosensitizer 2.4‐bis (1‐decyloxyethyl)‐Ca‐deuteroporphyI diaspartic acid (Ga ‐DP), 20 female Syrian golden hamsters with experimentally induced pancreatic cancer were irradiated with a pulsed Nd : YAG laser with a Q switch after administration of Ga ‐DP. To induce pancreatic cancer, N‐nitroso‐bis‐(2‐oxypropyI) amine (BOP) at 10 mg/kg body weight was injected subcutaneously once a week for eight weeks. Ten of the twenty animals served as a control group. The other ten received laser treatment beginning 20 weeks after BOP administration. Twenty‐four hours after intravenous injection of 3 mg/kg Ga‐DP, pulsed Nd : YAG laser irradiation was performed using a Q switch with 1 W of power output for 3–5 minutes at a frequency of 300 Hz. Elimination or necrosis of the entire tumor resulted with tumors 6–10 mm in diameter in 6 animals. In 3 animals which had tumors more than 12 mm in diameter, cancer cells remained at the margins of the treated area. These results were felt to not only reflect the thermal effect of laser therapy, but also the effect of PDT combined with Ga‐DP. They suggest that Ga‐DP could become a clinically valuable photosensitizer in combination with P