Abstract: A topical composition of a semi-solid consistency suitable is provided for transdermal application of prostaglandin E.sub.1. The composition comprises prostaglandin E.sub.1, 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 C.sub.1 to C.sub.8 alcohol, an aliphatic C.sub.8 to C.sub.30 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.