This study is a double-blind, placebo controlled, parallel design, Phase 2A study evaluating the potential activity and safety of a single administration of hMaxi-K (8000 or 16000 µg) or placebo (PBS sucrose 20%) injected into the corpus cavernosum of the penis in men who have been unable to tolerate, do not wish to continue, or have had unsuccessful results with, prior therapy for ED.