The study of DNA sequence variation at the population level is of much interest to population geneticists, molecular evolutionists, and systematists. There are many procedures for retrieving or generating useful indicators of DNA sequence variation in natural populations. However, the full analytical power of population genetics can only be applied to a subset of such indicators. The population genetic analyses are best utilized if the information gathered has the following characteristics: (1) the samples are sufficiently large and encompass several local populations across the area of interest, (2) the data consist of clearly defined orthologous sets, for example, haplotypes of specified regions of the mitochondrial genome and alleles of nuclear loci, and (3) the information includes frequencies and distributions of alleles (and haplotypes) and of genotypes, as well as the underlying sequence differences. Extensions to other organisms and genes, both nuclear and cytoplasmic, should be straightforward. © 1993, Elsevier Inc. All rights reserved.