A 50-year-old woman presented with CML-CP and was initially treated with branded imatinib (Glivec) 400 mg/day. She rapidly achieved a complete hematologic response (CHR), at which point she switched therapy to a copy version of imatinib (Imatib). She received 400 mg/day of Imatib for 3 months, during which time her platelet count decreased from 250 x 10(9) to 105 x 10(9)/L and her hemoglobin count fell from 12.8 to 11 g/dL. The patient's total leukocyte count rose rapidly from 4 x 10(9) to 70 x 10(9)/L, and the CHR was lost. At this point, therapy was switched back to Glivec at 400 mg/day, and the CHR was rapidly regained. Furthermore, the patient achieved a major cytogenetic response by 6 months after reintroduction of Glivec. This case report suggests a difference in clinical efficacy between the authorized form of imatinib (Glivec) and the copy version of the drug (Imatib). The exact reasons for the observed difference in clinical efficacy are unknown, but likely relate to the use of alternative polymorphic forms of the drug. Glivec can be obtained directly from the manufacturer (Novartis Pharmaceuticals) through a variety of patient access programs that should be fully explored when needed.