Photodynamic therapy (PDT) is a therapeutic modality for the treatment of tumors. This technique uses a visible light to activate a photosensitizer compounds, leading to a photo-oxidation process of biological tissue that can induce apoptosis or necrosis both in vivo and in vitro. However many of the cytotoxic effects remain an open question to be investigated. The cytotoxicity to specific cellular targets of classical photosensitizers used in the PDT in vitro has been analyzed in this work. The photosensitizing effects of Chloroaluminum Phthalocyanine Tetrasulfonate (AlPcS(4)) were studied on the mitochondria, cytoskeleton and endoplasmic reticulum of HeLa cells. The cells were irradiated with a diode laser (working at 670 nm; energy density of 4.5 J/cm(2 )and power density of 45 mW/cm(2)). The spectrofluorimetric analysis of the mitochondria showed changes in membrane potential. Cytoskeleton and endoplasmic reticulum showed basic alterations in distribution after PDT treatment, as an indicator of cellular death process.