Photochemical and phytophysical aspects of drug stability; technical requirements and equipment for photochemical stability and testing; standardization of photodegradation studies and kinetic treatment of photochemical reactions; is the photodecomposition of drugs predictable?; photodecomposition and stabilization of compounds in dosage forms; addressing the problems of light instability during formulation development; light activated drugs and drug formulations in drug targeting; benefits and adverse effects from the combination of drugs and light; screening of new drugs for ocular phototoxicity; the contribution of organic photochemistry to investigations of phototoxicity; in vitro screening of the photoreactivity of antimalarials - a test case; inconsistencies and deficiencies which exist in the current official regulations concerning the photolytic degredation of drugs; photostability testing - design and interpretation of tests on drug substances and dosage forms; mathematical models for studies of photochemical reactions; the application of photoacoustic spectroscopy to the photodegradation of drugs.