Based on previous evidence suggesting positive effects of fever on in vivo hematopoiesis, we tested the effect of hyperthermia on megakaryopoiesis (MK) in ex vivo cultures of CD34-enriched cord blood (CB) cells. The cells were cultured at 37 degreesC or 39 degreesC for 14 days in cytokine conditions optimized for megakaryocyte development and analyzed periodically. Compared to 37 degreesC, the cultures maintained at 39 degreesC produced significantly more (up to 10-fold) total cells, myeloid and MK progenitors, and total MKs, and showed accelerated and enhanced MK maturation with increased yields of proplatelets and platelets. This observation could facilitate clinical applications requiring ex vivo expansion of hematopoietic cells. (C) 2004 Wiley Periodicals, Inc.