Evidence from studies in rodents suggests that mate selection is influenced by major histocompatibility complex (MHC) haplotypes, with preferences for dissimilar partners. We initiated studies to determine whether avoidance of a mate with the same HLA haplotype as one’s own might be occurring in the Hutterites, a reproductive isolate of European origins. Previously, we reported a statistically significant deficiency of couples matching for 1 or more haplotypes among 411 couples with known HLA haplotypes defined by serology (Ober, Weitkamp, Cox, Dytch, Kostyu, & Elias, 1997). In this report, matching for 5-lo-cus, 11-locus and 16-locus HLA haplotypes defined by serological, molecular, and biochemical methods, we considered the same 411 couples. Using the same two methods for estimating the number of couples expected to match for a haplotype as we did in our earlier report, fewer couples than expected matched for a haplotype (first method, using population genotype frequencies, P = 0.0023-0.0035; second method, using computer simulations, P = 0.001-0.049). These results are consistent with the conclusion that Hutterite mate choice is influenced by HLA haplotypes, with an avoidance of spouses with haplotypes that are the same as one’s own.