The porphyrins seem to be the most effective photosensitizers in photodynamic therapy of cancer. Monomers and dimers of sulfonated and nonsulfonated porphyrins [5,10,15,20-tetra-phenyl-porphyrin, 5,10,15,20-tetranaphtyl- porphyrin (TNP), 5,10,15,20-tetra-p-sulfonato-phenyl-porphyrin (TS4PP) and 5,10,15,20-tetra-psulfonato- naphtyl-porphyrin], are studied in this paper by means of different spectral methods (UV-vis, fluorescence and polarization fluorescence). The porphyrins as TNP seem to be the most effective photosensitizer especially in a DMSO:water binary mixture of solvent. Monomer–dimer and J-aggregation equilibria and the temperature dependence of TS4PP spectra are also studied in this paper. The incorporation of the forms of these porphyrins into blood cells is studied by means of the cytofluorimetric method.