The possible role of thyroid hormones in the Nitric Oxide (NO)-mediated response to sexual stimulation, and on prostaglandin E1 (PGE1) and Sildenafil in the treatment of erectile dysfunction was investigated using the corpus cavernosum of the New Zealand rabbit animal model. The parameters studied were penile erection monitored as contractile force of the erectile tissue, sperm count and motility; in parallel with the haematocrit, red cell count or rheology, Heart Rate (HR), Mean Arterial Pressure (MAP), Thyroid Stimulating Hormones (TSH) and Thyroxine levels. Hypothyroidism or thyroidectomy was found to cause depletion of Endothelium Derived Relaxant Factor (EDRF) thereby causing very feeble contraction of the cavernosum muscle, in both prostaglandin E1 (PGE1) and sildenafil, oligospermia and less than 45 % motile sperms. Thyroxine treatment produced contraction proportionate to the concentrations of PGE1 and Sildenafil; providing evidence that the erectogenic actions of both PGE1 and Sildenafil are possible only in the presence of adequate thyroid hormone level.