Compounds that inhibit phosphodiesterase 1 (PDE1) are useful to treat glaucoma or elevated intraocular pressure. The PDE1 inhibitors may be administered as monotherapy or in combination with additional intraocular-pressure lowering agents. In addition, the invention provides ophthalmic compositions comprising PDE 1 inhibitors and optionally one or more additional intraocular pressure-lowering agents. Topical and systemic therapy may be used.