To study the effect of protein deficiency on collagen cross-Unking in albino-rat skins and granulomas, two groups of weanling albino rats were raised for 3 weeks with normal and low protein diets by paired-feeding technique. The analysis of skins showed α1and α2-chain subunits of neutral salt-soluble collagen appreciably increased, β11- and β12-chains and the aldehyde content significantly decreased whereas the solubility of insoluble collagen in KCNS, urea or pronase increased greatly in protein-deficient animals compared to controls. The gel reversibility of neutral salt-soluble collagen increased in both skins and granulomas of protein-deficient animals compared to controls. The results indicate that in protein deficiency the cross-linking and maturation of collagen are impai