The invention relates to a method for identifying a candidate agent for use in a medicament for diabetes or obesity said method comprising (i) providing a candidate inhibitor of PPM phosphatase, (ii) providing a first and a second sample comprising PPM phosphatase, (iii) contacting said candidate inhibitor with said first sample comprising PPM phosphatase, and (iv) assaying said first and second samples for PPM phosphatase activity, wherein said PPM phosphatase is selected from the group consisting of PPM1E, PPM1F, PPM1J, PPM1K, PPM1L and PPM1M, wherein if the PPM phosphatase activity is lower in said first sample than in said second sample then said candidate inhibitor is identified as a candidate agent for use in a medicament for diabetes or obesity, preferably type II diabetes. The invention also relates to the use of metformin and phenformin as inhibitors of PPM phosphatases.