Abstract: The present invention is directed to microbiocidal combinations and processes for inhibiting the growth of microorganisms. The novel combinations and processes of the present invention show unexpected activity against microorganisms, including bacteria, fungi and algae. Specifically, the combinations of materials which are to be added to a system at the time of their use comprise (i) an oxidant such as potassium monopersulfate, sodium perborate, hydrogen peroxide or sodium percarbonate, (ii) a microbiocide such as 2,2-dibromo-3-nitrilopropionamide, methylene bis thiocyanate, 5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one, tetrahydro-3,5-dimethyl-2H,1,3,5-thiadiazine-2-thione, and sodium dimethyldithiocarbamate/disodium ethylene bis dithiocarbamate and optionally (iii) a surfactant such as a fluorinated surfactant, and (iv) an anti-corrosive material such as an anhydrous phosphate, or combinations thereof.