Objective： To study the characteristics of immunophenotype in acute lymphoblastic leukemia （ALL） and its clinical significance. Methods： Immunophenotyping was performed on 81 ALL patients by three-color flow cytometry analysis using CD45/SSC gating, meanwhile the cytogenetic analysis was performed on 45 cases out of 81 ALL patients. Results： （1） CD19 was the most commonly expressed of all B-lineage antigens detected with the positive rate being 100%. In T-ALL, the positive expression rate of CD5 and CD7 was the highest, being 90%. Both B-ALL and T-ALL overlapped in expression of lineage antigens. There was no significant difference in the complete remission rate （CR rate） between T-ALL and B-ALL. （2） The incidence of ALL with rayeloid antigens expression （My＋ALL） was 39.5%. CD13 was most often seen among the myeloid markers. My＋ALL always involved in B-lineage antigens and the CR rate in children and adults was 72.2% and 78.6% respectively. （3） The incidence of HAL was 19.8%. Coexpression of B-lineage and myeloid-assoeiated antigens was the commonest subtype in HAL. The expression of CD34 was commonly seen in HAL patients （81.3%）. The CR rate was low in HAL, 50% for children and 40% for adults. （4） Compared to T-ALL, B-ALL, My＋ALL, and HAL had a higher positive rate of CD34 expression with the difference being significant （P〈0.025）. Conclusion： Immunophenotyping had remarkable predominance in diagnosing special category of ALL （such as HAL and My＋ALL）; CD19 and CD5 were highly sensitive in diagnosing B-ALL and T-ALL, but less special, and overlapping was found in expression. No significant association was found between the expression of CD34 or myeloid antigens and CR rate, while low CR rate was found in HAL patients, especially for those coexpressing CD34 antigen.
