A method for estimating the proportion of mutagens in a sample of N compounds is developed. For this procedure to be applicable, there must be a statistically significant correlation between the number of mutagens in the sample and the sample size N. Sample size is treated as a random variable. A sequential sampling scheme is considered. In the first stage, compounds are identified and classified as mutagens, nonmutagens, or untested, as reported in the literature. In the second stage, all untested compounds are tested for mutagenicity. Since data of this type are not generally available, estimates of the proportions of compounds tested (p), tested and mutagenic (p1), and untested but mutagenic (p2) are developed from existing compilations. It is shown that there is a high, statistically significant correlation between the total number of mutagens in a sample and the sample size N. The proportion of mutagens in a sample for various values ofp,p1andp2is tabulated.