The two-dimensional gel electrophoresis (2-DE) method developed by O'Farrell was used to analyze the differences of major proteins between lymphoblasts from children with acute lymphocytic leukemia (ALL) at diagnosis (lymphoblasts, n = 6), normal lymphocytes (n = 6) and lymphocytes from children with ALL in complete remission (lymphocytes in CR, n = 12). Among all the spots, those which were deeply stained and large were termed 'major spots'. Their number was 118. Two spots (No. B1 and B2) were characteristic of lymphoblasts, three spots (No. N1-N3) were characteristic of normal lymphocytes. In lymphocytes in CR, the latter spots were not always detected, and furthermore, the former spots were detected in several gels. These findings may relate to the insufficient recovery of functions of lymphocytes in CR. Several spots (No. 6, 55 and 57) in lymphoblasts were remarkably larger than those in normal lymphocytes. Spot No. 67, an actin spot, in lymphoblasts was smaller than that in normal lymphocytes. Spots No. 6, 55 and 57 in lymphocytes in CR were relatively small in size.