AbstractCytogenetic studies as well as erythroid and myeloid progenitor cell assays were performed in a 29‐yr‐old epileptic man with pure red cell aplasia (PRCA) who had been treated with primidone for several years. Despite clinical evidence of preleukemia, our studies indicated an underlying atypical Philadelphia chromosome‐positive myeloproliferative disorder. These laboratory findings were confirmed by the subsequent development of chronic myeloid leukemia (CML) which terminated in a CALLA‐positive lymphoblastic crisis 32 months later.The rare concurrent occurrence of PRCA and CML and the possible inducing role of the preceding antiepileptic treatment are di