Myeloproliferative neoplasms are a family of blood cancers that if left untreated can progress to bone marrow failure and acute myeloid leukemia. Inhibition of the protein JAK2 has emerged as potential therapy. However, this approach has thus far had limited success and been accompanied by significant toxicity. New research in mice suggests that JAK2 activity can be reduced by pharmacological targeting of the protein HSP90, which stabilizes JAK2.