Leukaemia-cancer cells have altered biochemical properties resulting in their high rate of growth compared to normal cells. One of these is augmented activity of enzymes called tyrosine kinases including members of the Src family. One called Lyn has been implicated in several leukaemias as well as cancer. We have identified a novel mechanism of down-regulating this family of enzymes mediated by small proteins. These may allow us to develop novel therapeutics for cancer-leukaemia treatment.