Ninety-eight Holstein cows from the I-O-State breeding research herd were serologically typed for class I bovine lymphocyte antigens. After exclusion of animals carrying alleles that occurred at frequencies lower than 4%, records from 82 cows that had 161 lactations remained for analysis of major histocompatibility complex allelic effects. A gene substitution model was used to evaluate the additive effects of nine alleles (frequencies of 4 to 20%) at the bovine lymphocyte antigen complex A locus on general health, udder health, and production traits. Allele w14(w8) was associated with decreased quarter milk sample California Mastitis Test scores, composite milk sample California Mastitis Test and Wisconsin Mastitis Test scores, decreased total health costs, and with increased milk yield, fat yield, fat percentage, and income over feed costs. Allele w11 was associated with decreased clinical mastitis, discarded milk, and udder health costs but was also associated with decreased fat yield, fat percentage, and income over feed costs. Allele w31(w30) was associated with decreased fat percentage. These relationships suggest that alleles at the bovine lymphocyte antigen complex A locus may serve as markers for health and production traits. Thus, the potential may exist for enhancement of disease resistance or production in cattle via marker-assisted selection and genetic manipulation techniques using class I genes of the bovine major histocompatibility complex.