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The use of antifoaming agents to break down high expansion foam was investigated in small scale tests, and three commercially available antifoaming agents were subsequently selected for large scale tests. In the latter tests about 2 l (0.4 gal) of a 5 per cent solution of the agents in water, when applied as a spray, broke down about 30 m^3 (1000 ft^3) of foam in 3 minutes; for these tests commercial garden spray equipment was used, with minor modifications. The antifoaming agents were considerably more effective than plain water, and were also effective against various high expansion foam concentrates at present on the market. Other factors investigated included variation of rate of application and solution strength of the antifoaming agents on the breakdown of foam. The spray technique was easy to acquire and economic to use.