The present invention provides crystalline (N)-((S)-2-hydroxy-3-methyl-butyryl)-1-(L-alaninyl)-(S)-1-amino-3-methyl-- 2,3,4,5-tetrahydro-1H-3-benzazepin-2-one, a crystalline anydrate and dihydrates thereof, compositions comprising (N)-((S)-2-hydroxy-3-methyl-butyryl)-1-(L-alaninyl)-(S)-1-amino-3-methyl-- 2,3,4,5-tetrahydro-1H-3-benzazepin-2-one, its crystalline anhydrate or dihydrate, and methods for using the same.