The goal of this study was to develop a strategy for the selective destruction of cancer cells by ultrasonic irradiation in the presence of an antibody-conjugated photosensitizer. To this end, a photoimmunoconjugate (PIC) was prepared between ATX-70, a photosensitizer of a gallium-porphyrin analogue, and F11-39, a high affinity monoclonal antibody (MAb) against carcinoembryonic antigen (CEA), which is often overexpressed in various carcinoma cells. This conjugate, designated F39/ATX-70, retained immunoreactivity against purified CEA and CEA-expressing cells as determined by enzyme-linked immunosorbent assay, flow cytometry and immunofluorescence microscopic analysis. The cytotoxicity of F39/ATX-70 against CEA-expressing human gastric carcinoma cells in vitro was found to be greater than that of ATX-70 when applied in combination with ultrasound irradiation. When in vivo anti-tumor effects in a mouse xenograft model were assessed, intravenous administration of F39/ATX-70 followed by ultrasonic irradiation produced a marked growth inhibition of tumor compared with irradiation alone or irradiation after administration of ATX-70. These results suggest that the PIC between anti-CEA MAb and ATX-70 may have applications in sonodynamic therapy where destruction of CEA-expressing tumor is required.