Based on progress in our understanding of the physiology of erection, intracavernous injections of vasoactive substances have completely changed the treatment of impotence. Essentially, erection results from the effect of smooth muscle relaxation in the vascular walls leading to local fall in vascular resistance and increased arterial flow combined with smooth muscle relaxation within the sinusoid spaces of the cavernous bodies. Smooth muscle cell tone is regulated not only by the classical norepinephrine and acetylcholine neurotransmitters, but also by other non-adrenergic and non-cholinergic neurotransmitters released locally. Although the "erectile neurotransmitter" has not been identified parasympathetic nerve terminaisons release nitric oxide (NO) a powerful myorelaxant agent. NO is also synthetized by the endothelial cells on the internal surface of the sinusoidal spaces. These recent findings have led to the use of papaverin to reduce the level of intracellular calcium, alpha-blockers to antagonize alpha-receptor and prostaglandin to inhibit norepinephrine release. Vasoactive intestinal polypeptide, a myorelaxing agent, and linsidomine which favours NO release have also been used. Diagnostic tests by intracavernous injections are indicated as part of the complete work-up in patients consulting for impotence. Therapeutic indications for auto-injections require careful choice of the agent and the dosage to inject depending on the cause of the impotence and the patient's demands and capacity to learn the technique. Papaverin or prostaglandin E1 alone or in combination with phentolamine give good results. Rigid erections can be obtained in over 60% of the patients. Alpha-blockers appear to be the least active in terms of rigidity. Mid-term results of intracavernous fibroses have been reported after papaverine injections. Priapism is the main secondary effect of intracavernous injections.