Silicone defoamers have been used successfully to eliminate the mucuscovered bubbles which obstruct a gastroscopist's view of the stomach. This led to their trial in treating patients complaining of flatulence and distention. Two hundred patients, aged 23 to 84 years, were given methyl polysiloxane, a physiologically inert silicone, for four weeks to three and a half years. Although other measures had not relieved symptoms, 40 mg. of methyl polysiloxane taken orally 4 times daily produced excellent or good results in 151 patients. In a control group of 20 patients who had had excellent or good results from the methyl polysiloxane, the substitution of a lactose placebo was followed by renewed complaints within 24 hours in 18 patients.