Methods and compositions for stimulating the growth of hair are disclosed wherein said compositions include a cyclopentane heptanoic acid, 2-cycloalkyl or arylalkyl compound represented by the formula I wherein the dashed bonds represent a single or double bond which can be in the cis or trans configuration, A, B, Z, X, R1 and R2 are as defined in the specification. Such compositions are used in treating the skin or scalp of a human or non-human animal. Bimatoprost is preferred for this treatment.