Open-Label Phase 3 study to evaluate the long-term safety and efficacy of udenafil, an orally administered selective inhibitor of PDE-5 for the treatment of subjects with erectile dysfunction (ED).

Patients completing the double-blind phase will be entered into Study 01409 at the intermediate dose. Up and down dose adjustments will be allowed.

Inclusion Criteria:

• Subject has completed Study PR-01209 or PR-01309
• Continues in a stable monogamous relationship with a consenting female partner who is at least 19 years of age.
• Partner is not pregnant or lactating

Exclusion Criteria:

• Symptomatic coronary artery disease, myocardial infarction or cardiac surgical procedure.
• Cardiac arrhythmias requiring antiarrhythmic treatment
• Symptomatic congestive heart failure
• Taking nitrate medication in any form
• Uncontrolled diabetes (HbA1c ≥ 13%)
• Hypersensitivity to phosphodiesterase type 5 (PDE-5) inhibitors