This International Standard specifies a method for the determination of the soluble nitrogen content of animal feeding stuffs after treatment with pepsin in dilute hydrochloric acid. This method does not distinguish between protein nitrogen and non-protein nitrogen. NOTES 1 The values obtained on using this method have no direct connection with digestibility in vivo. 2 If non-protein nitrogen is to be excluded from the test result, its content should be determined using an appropriate method.