The authors induced pulmonary silicosis in albino rats by the intratracheal method with 50 mg mixed middling slime from Panaguiriste and quartz dust, dissolved in I ml physiological solution. The animals received a single treatment and were killed on 90th day of the experiment. Some intime characteristics of collagen-forming mechanisms in lungs were followed up via routine histological, histochemical, enzymohistochemical/ acid phosphatase activity, beta-glucoronidase, AS-esterase and lipase/ and autoradiographic/H3 labelled proline/ methods. It was established, that under the effect of both dusts from Panaguiriste mines studied/ mixed dust and pure quartz dust/ considerable deviations developed in the structure of the lungs of the experimental animals in the enzyme activity of acid phosphatase and carbon esterase, accompanied by various forms of fibrosis in the organ, depending on the dust applied. The difference in the composition of both dusts quartz and mixed dust slime - had an effect on the degree of the deviations, but not on their character, manifested in: I. specific protective reaction of organism, with activation of the ferments from the group of carbon esterase in macrophagic elements of interstitium and around the silicotic alterations in the lungs of the experimental animals; 2. inhibition of the maturation of macrophages in silicotic foci and 3. acceleration of the proliferation of fibroblasts with intensification of collagen-formation, accompanied by an enhanced activity of the ferments from the group of carbon esterase and in the cytoplasm of fibroblasts. The authors draw the conclusion that the complex use of routine histological, histochemical and quantitative isotope methods enables the more significant determination of fibrinogenicity of quartz-containing dust even at the early terms of their exposure under experimental conditions.