The efficacy of photodynamic therapy (PDT) mediated by aluminium phthalocyanine (AlPc) and its mono- and disulphonated derivatives (AlPcS1 and AlPcS2, respectively) on murine EMT-6 tumour were compared in vivo. AlPc (0.25 mumol/kg) PDT resulted in no tumour recurrence in all treated mice. In contrast, PDT with AlPcS1 (2 mumol/kg) and AlPcS2 (1 mumol/kg) only produced tumour cure in 75% and 86% of mice, respectively. Immediately after AlPc-PDT, tumour cells were found to be viable as determined by in vitro clonogenicity, but progressive cell death occurred thereafter. In contrast, AlPcS1 and AlPcS2 PDT produced substantial cell death (approximately 35% and 70%, respectively, of entire tumour) immediately after phototherapy, and yet further loss of tumour cell viability continued after PDT. In all cases, few vascular effects were observed at 0 h post-PDT, as indicated by the retention of 99mTc-MIBI in the tumour. However, the reduction of blood flow in tumours progressed with time, such that blood flow in tumours fell to approximately 25% of the control level by 24 h after both AlPc and AlPcS1 PDT. With AlPcS2, there was only an approximate 50% fall in tumour blood flow by 24 h. These results demonstrate a greater PDT efficiency with AlPc on tumour destruction, which is an indirect mechanism involving damage of tumour vasculature, whereas AlPcS2 has a greater effect on direct tumour cytotoxicity and AlPcS1 exerts both direct and indirect modes of action against tumours.