The invention relates to a method for controlling hydrophobic particles in aqueous environment in paper or board manufacture. The method comprises preparing an aqueous stock comprising natural fibrous material, feeding the stock to a wire section, where a fibrous web is formed by draining excess water through a wire, and adding a control chemical to aqueous environment at least in one dosage point between the preparation of the stock and the exit of the web from the wire section. The control chemical comprises performic acid, which is added to the aqueous stock, which has consistency of at least 3 weight-%.