Abstract: The invention relates to methods for assaying LKB1 activity comprising providing a sample comprising LKB1, contacting the sample with a substrate kinase under conditions that permit phosphorylation, and monitoring incorporation of phosphate into the substrate kinase, wherein the incorporation of phosphate into the substrate kinase indicates LKB1 activity. Preferably the substrate kinase is or is derived from AMPK. The invention also relates to use of AMPK in the treatment or prevention of certain disorders, and to the use of AMPK in the manufacture of medicaments for certain disorders, and to the use of LKB1 in the activation and phosphorylation of AMPK. The invention also embraces yeast cells with certain genetic alterations relating to AMPKK and AMPK.