Visit 1: The subject will be offered, at random, for 4 attempts at home, either a combination dose regime (Viagra®50mg & Levitra®10mg, 4 tablets each) or 4 tablets of Viagra®100mg single dose or 4 tablets of Levitra® 20 mg. The subject will also receive 6 SEP (Sexual Encounter Profile) diaries to fill out at home after each sexual attempt. After 4 attempts the subject will return for visit 2, will respond to the same questionnaires and an additional EDITS (Erectile Dysfunction Inventory of Treatment Satisfaction) questionnaire. A new visit will be rescheduled for 2 weeks later to allow a washout period. At visit 3 they will receive the 2nd regime and 4 new SEP diaries, and after 4 attempts will return to visit 4, fill out the same 4 questionnaires. Again, a new visit will be rescheduled for 2 weeks later to allow a washout period. On visit 5 they will return to receive the third treatment regime. Again, they will receive 4 SEP diaries to fill out after each sexual attempt at home. At their final visit (visit 6), in addition to the other 4 questionnaires, the patients will be required to respond to a preference questionnaire regarding the preferred regime.