In many studies of longevity in experimental animals, sample sizes are small enough to warrant the use of statistical tests of significance in making judgments of scientific interest. Illustrated in this paper is a nonparametric test procedure for deciding on the statistical significance of observed differences in two empirical survival functions. This procedure takes an experimenter one step beyond comparing means and medians. For experimenters who wish to pursue the subject further, a brief entry into the extensive literature on survival analysis is also provided.