A method for developing Prostaglandin F.sub.2.alpha. analogs for enhancing and sustaining the growth of eye lashes. The exemplary method first provides a method for determining the ability of a FP receptor agonist test compound having unknown hair growth ability to induce hair growth in its free acid form. The test compound may then be provided in its amide, or slowly hydrolyzing form and ester form, or rapidly hydrolyzing form to determine the relative hydrolysis rate within corneal tissue. Depending upon its hair growth ability and relative hydrolysis rates, the Prostaglandin F.sub.2.alpha. analog in one or more forms may be used an ingredient in a binary cosmetic prodrug designed for enhancing and sustaining the growth of eye lashes.