Changes in collagen structure resulting in etching connective tissue in concentrated NaOH solution and possible effects on reconstitution of fibrils and fibres from collagen solution under the influence of glycosaminoglycans (GAGs) were examined. Collagen was isolated from bovine hide scraps, etched for 24 h in a 10% NaOH solution saturated with anhydrous sodium sulphate. GAGs solutions were isolated from bovine tracheas. The effect of GAGs interactions with collagen in the systems at ionic strengths of 0-0.7 Debye, modified with NaCl at pH 3-8, was evaluated visually by comparing the quantity of fibres, measuring the absorbance of the system at 400 nm and determining the content of proteins in the supernatant after centrifugation. The addition of GAGs to the collagen solution resulted in immediate formation of fibres and determining the content of proteins in the supernatant after centrifugation. The quantity time of reconstitution of the fibres increased with the quantity of GAGs added and the concentration of collagen. The optimal medium for the reconstitution of fibrils or collagen fibres under the influence of GAGs was pH 3 in the absence of NaCl. Collagen dissolved in chloride acid can be completely precipitated using crude GAGs isolate if the weight ratio of reagents, collagen:GAGs, is 1:0.3. The increase in ionic strength of collagen solution did not stimulate the formation of fibres, but induced turbidity due to the presence of small flocks and an increase in viscosity of the system, regardless of the concentration of GAGs.