The　purpose　of　current　study　was　to　investigate　the　potential　repeated　dosed　toxicity　of　ZnPcP2S2-based　photodynamic　therapy　(ZnPc-PDT)　in　Beagle　dogs.　Twenty-four　Beagle　dogs　were　randomly　allocated　to　four　groups,　in　which　they　were　administered　ZnPcS2P2　preparation　intravenously　at　dosages　of　0,　0.5,　1.5,　and　4.5　mg/kg　body　weight　and　then　were　irradiated　with　670　nm　laser　for　6　min　at　subsequent　48　and　72　h,　once　every　four　days　for　successively　10　times.　There　were　no　abnormal　changes　in　clinical　observations.　After　the　administration　most　animals　showed　dysphoria　and　several　had　light　edema　on　their　faces.　The　results　showed　no　mortality　and　no　abnormity　in　ophthalmoscopy,　electrocardiography,　hematology,　blood　biochemistry　and　urinalysis,　except　that　some　statistical　changes　in　specific　indexes　such　as　APTT　in　1.5　and　4.5　mg/kg　groups,　and　these　changes　disappeared　at　the　end　of　recovery.　Histopathological　examination　showed　hepatic　spotty　and　lytic　necrosis　in　Beagle　dogs　of　4.5　mg/kg　group,　and　at　the　end　of　recovery　the　damages　alleviated.　Additionally,　some　Kelly　and　Khaki　granules　presented　in　liver,　spleen,　lungs,　kidneys,　ovaries,　lymph　nodes,　marrows　and　injection　points.　These　drug　pigmentations　will　provide　valuable　information　about　distribution　of　ZnPcP2S2.　Based　on　the　results;　the　NOAEL　was　considered　to　be　1.5　mg/kg　and　ZnPc-PDT　appears　to　be　a　safety　and　promising　approach　in　clinic.　©　2006　Elsevier　Inc.　All　rights　reserved.