15-Keto fluprostenol isopropyl ester and 15-keto fluprostenol have demonstrated a stimulatory effect on the growth and thickening of the eyelashes without the disadvantages of the prostaglandin derivatives of the PGF2α group, which have a hydroxyl group at position 15 in their structure. The two 15-ketoderivatives have the same efficacy as the 15-hydroxyl derivatives in allowing the regrowth, lengthening, darkening, or thickening of the eyelashes, but without darkening the edge of the eyelid or coloring the iris, even temporarily.