Many immunologic studies of acute lymphocytic leukemia (ALL) during the past decade have demonstrated the close correlation of immunologic phenotypes of ALL subclasses with the clinical presenting features and prognosis. However, the clinical application of conventional immunologic techniques had been very limited because of the requirement of a fresh sample to prepare the mononuclear cell suspensions for study. We studied 81 cases of ALL using immunoperoxidase stain for nuclear terminal deoxynucleotidyl transferase (TdT) and immunoalkaline phosphatase stain for surface markers (using monoclonal antibody J5 for common ALL antigen [CALLA], Leu-1 for pan-T antigen, and B1 for pan-B antigen) on air-dried smears. The cases were classified as common ALL (TdT+, CALLA+, pan-T-, and pan-B-) (41 cases), null-ALL (TdT+, CALLA-, pan-T-, and pan-B-) (19 cases), T-ALL (TdT+, CALLA-, pan-T+, and pan-B-) (nine cases), B-ALL (TdT-, CALLA-, pan-T-, and pan-B+) (six cases), pre-B-ALL (TdT+/-, CALLA+, pan-T-, and pan-B+) (four cases), or pre-T-ALL (TdT+, CALLA+, pan-T+, and pan-B-) (two cases). This subtyping of ALL correlated well with known clinical presenting features, prognosis, chromosome analysis in 35 cases with an abnormal clone, and conventional immunologic typing in 38 cases. The data suggest that these simple and practical immunocytochemical stains can be used for immunologic subclassification of ALL.