Abstract: The invention provides methods of treating erectile dysfunction comprising the step of placing within the fossa navicularis of the patient an effective erection-inducing amount of a prostaglandin E1 composition of a semi-solid consistency, as well as suitable applicators. The composition comprises prostaglandin E1, a penetration enhancer, a polysaccharide gum, a lipophilic compound, and an acidic buffer system. The penetration enhancer is an alkyl-2-(N,N-disubstituted amino)-alkanoate ester, an (N,N-disubstituted amino)-alkanol alkanoate, or a mixture of these. The lipophilic compound may be an aliphatic C1 to C8 alcohol, aliphatic C2 to C30 ester, an aliphatic C8 to C30 ester, or a mixture of these. The composition includes a buffer system capable of providing a buffered pH value for said composition in the range of about 3 to about 7.4.