Tables by Halvor-son and Ziegler (1933: Burgess Publishing Company, Minneapolis, Minn.) for estimating bacterial populations from results of successive dilution procedure, give the modes of Bayes "inverse probability" distributions. Since these distributions have varying degrees of skewness, such modal estimates are not comparable among themselves on any simple basis; and in the laboratory they have been found to exhibit systematic bias as compared with plate counts. In this paper, formulas are listed for computing geometric mean estimates. Three sample computations are compared with corresponding modal estimates (H. and Z.); they are found to be in better agreement with plate-counts. It is hoped that it will be possible in the near future to prepare comprehensive tables for practical use.