In mixed culture of lactobacillus hilgardii X(1)B and Leuconostoc oenos X(2)L, isolated from Argentinian wines, an amensalistic growth response was observed: Leuconostoc oenos did not grow, and after 24 h of incubation at 30 degrees C no viable cells were detected. In pure and mixed cultures, Lactobacillus hilgardii produced hydrogen peroxide early in the growth cycle, reaching the maximum at 24 h. The values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for the action of hydrogen peroxide on the growth of Leuconostoc oenos were: 4.08 mu g ml(-1) and 17.00 mu g ml(-1) respectively.