1- or 2- or 7-(substituted)-3-(optionally hetero)arylamino-[1H,2H]-pyrazolo[3,4-d]pyrimidine-4,6(5H,7H)-dione derivatives, in free, salt or prodrug form, are useful as pharmaceuticals, particularly as phosphodiesterase 1 inhibitors, useful for the treatment of diseases involving disorders of the dopamine D1 receptor intracellular pathway, such as Parkinson's disease, depression, narcolepsy and damage to cognitive function, e.g., in schizophrenia or disorders that may be ameliorated through enhanced progesterone-signaling pathway, e.g., female sexual dysfunction.
