Heterocyclic compounds useful for stimulating/inducing the growth of keratinous fibers, notably human hair/eyelashes, and/or slowing the loss of same, have the following structural formula (I) or salt thereof: ##STR00001## in which Hy is a heterocycle of 4 to 7 atoms, optionally comprising carbonyl/thiocarbonyl functional groups, and G is O, S or NH.