Abstract A manometric method using the Warburg apparatus has been investigated as a possible screening technique for the evaluation of agents used as preservatives in pharmaceutical preparations. This procedure also was utilized to determine the relative effectiveness of different preservatives, and preservative-surfactant combinations. The respiratory effects on baker's yeast were determined with methyl-paraben, propylparaben, and sorbic acid, separately, and each in the presence of polysorbate 80. Each of the three preservatives caused a decrease in oxygen consumption by baker's yeast. In general, the order of effectiveness was propylparaben > sorbic acid > methylparaben. Polysorbate 80 decreased the effectiveness of each of the three preservatives. Sorbic acid was the least affected, except at a preservative concentration of 0.025%. These manometric results are rapidly obtained, informative, and in general agreement with results found by more time-consuming procedures.