Often, arbitrary and capricious criteria are employed when sample sizes are selected, resulting in samples which are either too small sizes are selected, resulting in samples which are either too small to enable the evaluator to detect the hypothesized treatment effect or so large that human and financial resources are wasted. The tables described present the minimum number of cases needed for obtaining statistical significance between two proportions; one table reports value for a .05 significance level and another table is for a .01 significance level. In addition to presamples and postsamples, these tables can be used for determining the sample size for any two groups. In a similar fashion, given a certain number of cases, the tables can be used to determine what differences in proportions would be statistically significant. When using the tables, however, a minimum number of cases is necessary in each sample to obtain statistically significant differences between two proportions. The two tables and the formulas used are included.