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 the presence or absence of a double bond which can be in the cis or trans configuration and A, B, Z, X, R1 and R2 are as defined in the specification and a penetration enhancer. Such compositions are used in stimulating hair growth of human or non-human animals.