This paper contains results of a study on HLA-DR antigens in Chinese-American families. DR2, DR4, DRw9, and DRw6Y were the most common DR specificities encountered, and DR1 occurred with the lowest frequency. All recognized DR antigens were observed. The frequency of a blank allele was 6.4-12.8%. Weak serologic reactions with sera primarily of Caucasian origin were not infrequently observed. These findings suggested that ethnic-related antigens were present in this population. Two families showed segregation of a new serologic pattern based on polyspecific sera. The gene frequencies of the BfF allele and the GLO1 allele were low as compared to Caucasians. A method is described for improving the yield of viable B cells from frozen B-lymphocyte preparations.