This paper concerns the use of deep-red light absorbing chromophores as potential photosensitizers for photodynamic therapy (PDT). In setting the scene, the role of scattering by tissues and of the availability of convenient laser light sources are considered. In terms of long wavelength extremes for the production of singlet oxygen, it is pointed out that the energy gap between S1 and T1 (EST) is the critical factor. Some of the photophysical and photochemical properties of naphthalocyanines and octabutoxyphthalocyanines are presented. Both species absorb strongly at 740 nm and beyond. Finally, the tissue distribution and phototherapeutic effectiveness in animal tumor models is outlined. Delivered doses as low as 0.5 mg/kg body weight are optimally effective.