The invention provides a method of diagnosis or prognosis of preeclampsia in a pregnant subject, comprising providing a sample from a pregnant subject and measuring the ratio between the amount of (a) one or both of sFlt-1 and PlGF, and (b) one or both of a breakdown product of heme and a breakdown product of arginine, in the sample. Also described are assay kits and a computer adapted for use in the method. Also described is a method of treating preeclampsia, comprising administering a pharmaceutically effective amount of L-arginine and/or citrulline and an inhibitor of arginase or pharmaceutically acceptable salts thereof. Also described is a method of treating cancer, comprising treating a subject with a therapeutically effective amount of an anti-VEGF compound, L-arginine and an arginase inhibitor.
