A method for producing protein compositions comprising fibrinogen and fibronectin is disclosed, wherein a fibrinogen and fibronectin-containing starting solution is treated with a precipitating composition which comprises two different components that modify the solubility of fibrinogen and/or fibronectin, so that in a single-step precipitation a precipitate is formed which comprises fibrinogen and fibronectin, and the precipitate formed optionally is further treated by methods known per se.