An apparatus is described for generating and assessing foams in digestive fluids in vitro. The effects of caraway, cinnamon, dill, orange and peppermint oils on gastric and intestinal foams were examined. Reductions in foam volume were observed in every case, although the effects were not as great as those produced by a combination of dimethicone and silica. m-Cresol, p-hydroxybenzaldehyde, isobutanol, menthol and phenoxyethanol also reduced foam volume, but anti-foaming activity could not be related to published data on the ability to produce a 50% inhibition of a standard response in guinea pig ileum to carbachol. It is suggested that carminative action is a combination of effects, one of which is a reduction of gastrointestinal foam.