Abstract: Modified asphalt cements comprise asphalt cement, reacted tall oil, tall oil pitch, tall oil derivatives or mixtures of these, and polymers selected from block copolymers and latexes, both synthetic and natural. Methods of manufacturing include: blending a reacted tall oil-modified asphalt cement with a polymer-modified asphalt cement to obtain the desired properties; modifying an asphalt cement with a reacted tall oil, tall oil pitch, tall oil derivatives or mixture thereof, and then adding the selected polymer(s) to this tall oil-modified asphalt cement; modifying the asphalt cement with the selected polymer(s) and then adding the tall oil, tall oil pitch, tall oil derivatives and mixtures thereof and reacting with a strong base; and, adding the polymer(s), tall oil, tall oil pitch, tall oil derivatives and mixture thereof and the strong base all to the asphalt cement at or nearly at the same time.