Dried crude filtrate (DCF) from Streptomyces sp., containing antibiotic P-9, was compared in 1962 with a mixture of nickel chloride and zineb and in 1964 with symmetrical dichlorotetrafluoroacetone (DCTFA) for the control of cereal rusts on Marquis wheat. Seven applications of DCF gave significantly better control of stem rust on the sheaths than six applications of nickel–zineb. The control of stem rust on the necks and of leaf rust was equally good for both materials. Rust control by either material resulted in a substantial improvement of yield and grade. When 280 kg/ha of DCF, a quantity equal to that used successfully in three applications over a period of 4 weeks, was applied in a single application, less control was obtained and some phytotoxic necrosis occurred. The phototoxicity may have been due to an extraneous substance in the DCF, and might not be a limiting factor with purified or partially purified preparations.Under the conditions of the experiment in 1964, DCTFA was not as effective as DCF in rust control.