Totally 436 Chinese patients having received multiple transfusions of red cells and platelets on more than three occasions were screened for red cell antibodies. Twenty-six (6%) of them were positive. Anti-E, -Mia, and -c were the common alloantibodies. Nine patients were immunized during the period of regular transfusions, with a newly immunized rate of 2% (9/436). Among 436 patients, 387 were screened for HLA antibodies by lymphocytotoxicity test (LCT). The overall positive rate was 35%. Most of the antibodies identified were against the high-frequency HLA antigens in the Chinese population. About 10% of the LCT-positive cases reverted to negative state during the follow-up period. After chloroquine stripping of the target platelets, mixed passive hemagglutination assay was used to detect platelet antibodies other than HLA antibody. Fifty-eight of 161 cases (36%) were positive for platelet antibodies, but half of them disappeared within 1 month. Nineteen of the 58 patients had sepsis and 2 had jaundice. These findings suggested that HLA and platelet antibodies are common among Chinese, though their clinical significance and the role in platelet damage are doubtful.