Anabaptist history is a chronicle of repeated migrations, fissions, and fusions of various subgroups. The effects of these events should be evident in the population biology of the Anabaptist groups. No prior genetic studies have included the polymorphic and highly informative immunoglobulin markers. Here, 685 serum samples representing 1 Amish and 3 Mennonite community samples (7 congregations) were studied for immunoglobulin allotypes. The haplotypes IGHG*F B, IGHG*A,Z G, and IGHG*A,X,Z G range in frequency from 0.542 to 0.765, 0.123 to 0.290, and 0.075 to 0.170, respectively. IGK*1 frequencies range from 0.035 to 0.077. All frequencies are within expected ranges for central and western European population samples. There was considerable intergroup variability among the Anabaptist samples that was statistically significant (chi29 = 22.63, 0.005 < p < 0.01). Principal component analyses, including the immunoglobulin allotype frequencies and published data on ABO, MN, and Rhesus (Dd) markers, demonstrate that the Mennonite congregation samples with close historical ties group together and are distinct from the Amish and Meridian congregation samples.