A patient is described who, during a three-year illness, exhibited multiple phenotypic expressions of leukemia. She was diagnosed initially as having acute lymphoblastic leukemia (ALL) followed by chronic myelogenous leukemia (CML) one and a half years later. Subsequent blast transformations were lymphoblastic, but preterminally, a myeloblastic transformation occurred. These later leukemias probably were not chemotherapy induced, because a review of her initial work-up revealed the presence of a smaller G group chromosome in 1 of 20 metaphases examined. Her clinical course also differs from the CML that presents in lymphoid blast crisis because the Philadelphia chromosome only was emerging at that point. This case illustrates the interrelationships of the various leukemias and supports the hypothesis that a totipotent stem cell may undergo leukemic transformation resulting in variable and simultaneous expressions.