Energetically differing rations which received ca. 45% of their crude protein from a supplement of soybean oil meal or urea were tested in a model experiment with adult wethers fitted with duodenal re-entrant cannulae or rumen cannulae resp. The N-equivalent exchange of soybean oil meal by urea in wethers resulted in a distinct increase of the NH3-N content of the rumen fluid, an increase of irreversible N losses and thus a worsening of the utilization of the available N for bacterial N-efficiency. A significant influence on duodenal NAN passage, on the apparent fermentation of the organic matter, on postruminal NAN digestibility and on the content of amino acid nitrogen as well as the amino acid composition of the duodenal NAN could not be detected. The increase of the energy level of the rations did not have a significant influence on the parameters of the ruminal N metabolism in the wethers. The studies with calves and adult wethers showed that a transposition of the parameters of ruminal N metabolism obtained to calves is not possible under the conditions given.