Collagen is a widespread body constituent that is affected by estrogen status in women. Its decrease after menopause can be prevented and/or restored by estrogen treatment. We explored the effect of four different hormonal replacement regimens on total skin collagen content by measuring hydroxyproline in skin biopsy specimens taken from postmenopausal women. All regimens showed increases in skin collagen levels proportionate to the levels at the start of the treatment. Estrogen replacement therapy is shown to be prophylactic in women who have higher skin collagen levels and both prophylactic and therapeutic in women with lower skin collagen levels.