The invention provides a human PDE1A which is associated with the cardiovascular disorders, endocrine system and hormone disorders, cancer disorders, gastrointestinal and liver diseases, hematological disorders, respiratory diseases, neurological disorders and urological disorders. The invention also provides assays for the identification of compounds useful in the treatment or prevention of cardiovascular disorders, endocrine system and hormone disorders, cancer disorders, gastrointestinal and liver diseases, hematological disorders, respiratory diseases, neurological disorders and urological disorders. The invention also features compounds which bind to and/or activate or inhibit the activity of PDE1A as well as pharmaceutical compositions comprising such compounds.