Abstract: An ultraviolet sterilization and disinfection system for fluids which includes apparatus for sensing selected operating characteristics such as physical characteristics of the fluid to be disinfected or sterilized and the operating conditions of the ultraviolet sources proportioning these variable and generally non-linear parameters and modifying such factors as fluid flow, ultraviolet energy imparted to the fluid to insure destruction of selected organisms without the use of excessive energy. Control may also be provided for the admission of selected quantities of disinfecting chemicals such as chlorine to the fluid.