The influence of hypertensive regime on collagen synthesis in glomerular basement membranes of rats was studied. Isolated glomeruli were incubated in a medium containing <sup>14</sup>C-labeled proline. It was demonstrated that there was a higher proline incorporation and proline conversion to hydroxyproline in rats kept on the hypertensive regime. However, solubilization of the collagenous fraction by limited pepsin digestion did not reveal any qualitative changes in the collagen type deposited. It is concluded that the DOCA-NaCl treatment in rats results in an intensive accumulation of collagen, mainly of type IV, typical for basement membranes.