To determine the onset of action, safety and toleration of different formulations and doses of UK-369,003 in patients with erectile dysfunction. Patients should have been previously treated with PDE5 inhibitors and have been responders to the drugs. Duration of treatment is 4 weeks.

Inclusion Criteria:

• Erectile dysfunction as defined by DSM-IV. Patients should have been PDE5 inhibitor respondents

Exclusion Criteria:

• Alpha blockers and Nitrates of any preparation