Ten members of a white American family, spanning three generations, were studied. Three family members from two different generations were affected with hair loss. Two had alopecia universalis; one had alopecia areata. All subjects were HLA-typed using 131 antiserum samples obtained from multiparous female donors defining 41 HLA-A and HLA-B antigen specificities. Six haplotypes were identified. The affected persons and four other family members shared a common haplotype, HLA-A2,B40. The OKT4 (helper), OKT8 (suppressor-cytotoxic) cells, OKT4-OKT8 (helper-suppressor-cytotoxic) ratios and the percentage of B cells found were comparable for both the 12 control subjects and the family members studied. However, family members showed increased autoantibody formation, decreased T-cell percentages, and concanavalin A-induced suppression of the normal lymphocyte response to mitogens.