We investigated the significance of p210 and p190 molecular abnormalities in 32 adults with Philadelphia chromosome (Ph)-positive acute leukemia. p210 was detected in 15 patients (47%), p190 in 16 (50%), and both in one (3%). p210 was noted in 11 of 24 patients (46%) with acute lymphocytic leukemia, and in four of eight patients (50%) with acute myelogenous or undifferentiated leukemia. Among 29 patients with untreated disease (p210, 14 patients; p190, 15 patients), no significant differences in the two molecularly distinct groups were observed by pretreatment characteristics including age, degree of organomegaly, anemia, leukocytosis, thrombocytopenia, occurrence of karyotypic abnormalities in addition to Ph, or residual diploid metaphases. Complete response (CR) rates were also similar. Although the remission duration tended to be longer with p190 (P = .08), the differences were minor (median duration 29 v 20 weeks) and not paralleled by differences in survival rate. In 10 patients studied by karyotypic analysis in remission, two of four patients with p190 and two of six patients with p210 showed 100% normal metaphases. One of the seven patients (14%) with p210 who achieved CR manifested a morphologic picture of second chronic-phase chronic myelogenous leukemia lasting for 1 month. We conclude that the molecular studies in Ph-positive acute leukemia are not associated with significantly different clinico- laboratory, karyotypic, or prognostic implications.