This invention relates to novel amorphous losartan potassium, novel losartan potassium in a crystalline form that is a hydrate, novel crystalline losartan potassium Form IV and solvates thereof, novel crystalline losartan potassium Form V and solvates thereof, to processes for their preparation, to compositions containing them and to their use in medicine. This invention further relates to a novel process for preparing crystalline losartan potassium Form I and Form II.