Materials and methods for reducing cell proliferation or extracellular matrix production in a mammal are disclosed. The methods comprise administering to a mammal a composition comprising a therapeutically effective amount of a zvegf4 antagonist in combination with a pharmaceutically acceptable delivery vehicle. Exemplary zvegf4 antagonists include anti-zvegf4 antibodies, inhibitory polynucleotides, inhibitors of zvegf4 activation, and mitogenically inactive, receptor-binding variants of zvegf4. The materials and methods are useful in the treatment of, inter alia, fibroproliferative disorders of the kidney, liver, and bone.