Published at: US- Egypt science and technology agreement, Workshop on Laser Chemistry and applications to materials and biomedical research, National Research Center, Cairo, 2004 Abstract This paper throw light on laser, natural and artificial photosensitizers in agriculture, the difference between photosensitizers and sunburn has been discussed. Mode of action and role of photosensitizers as photo- pesticides against noxious insects, e.g., mosquito larvae, house flies, etc. have been explained, role of photosensitizers photo-dynamic - therapy has been clarified. The photosensitization problem in livestock and their clinical signs have been discussed. This line of research needs more creative work and collaboration between researchers in different disciplines to promote the science of photobiology and its application against insect pests and microbes to the benefit of Human and animal health.