A method of selecting/identifying an active agent for modifying the shape of keratin fibers, includes the following steps: a) culturing mammalian cells, b) adding a test substance to the mammalian cell culture, c) after incubation thereof, assaying the amount of glycosaminoglycans (GAGs) in the mammalian cells or in the mammalian cell culture medium, d) comparing the amount of GAGs measured in step c) with that measured starting from a control culture of mammalian cells, obtained under the same conditions, but in the absence of test substance, and selecting the substances for which the amount of GAGs is modified by at least a factor of 0.5 relative to the amount measured in the control culture； the active agents thus selected/identified are useful for modifying the shape of keratin fibers.
