This paper emphasizes the practical aspects of photocatalysis as applied to practical problems of some concern and employs semiconductor dispersions of CdS and TiO2. It presents our recent contributions to (i) the photocleavage of hydrogen sulfide, (ii) the treatment of wastes, and (iii) the photoreduction of and recovery of metals on TiO2. It further stresses the point that our present knowledge of photocatalysis and photocatalytic processes can be and must be applied to resolving environmental problems caused by discharge of toxic materials into the aquatic and atmospheric ecosystems. The problems are many; they must be addressed.