Disclosed are compositions for stabilizing a source of active halogen in aqueous solution. The compositions comprise (i) at least one substituted N-hydrogen compound, such as 5,5-dimethylhydantoin, and (ii) at least one additional nitrogen compound selected from ammonia, ammonium salts, and nitrogen compounds containing no carbon-hydrogen bonds, the molar ratio of (i) and (ii) being in the range of 50:1 to 0.02:1. Active halogen-containing aqueous solutions stabilized by the above compositions are particularly useful for controlling microbial and planktonic growth in aqueous systems such as process liquids in the pulping or papermaking industry. The compositions are also useful in reducing the corrosivity of halogen-containing solutions.
