The acid form of vitamin A (retinoic acid; RA) is used to treat a type of leukemia known as acute promyleocytic leukemia (APL). It works by binding to its receptors (retinoic acid receptors, RARs) and driving the leukemic cells to mature and die, rather than remain blocked at a highly proliferative immature stage of development. Researchers from the Fred Hutchinson Cancer Research Center in Seattle have now shown that a protein complex known as CaMKII inhibits RAR activity and that CaMKII inhibitors drive leukemic cells to mature and die.