Data set of forage samples (n = 6) was used for evaluation of nitrogen fractions in ruminant nutrition. The samples were analysed for individual nutrients and gross energy value. Individual nitrogen fractions were determined by following laboratory methods: determination of non-protein nitrogen (NPN), determination of insoluble protein (IP) and soluble protein (SOLP), determination of nitrogen insoluble in acid detergent (ADD3) and determination of nitrogen insoluble in neutral detergent (NDEP). From these values were calculated fractions A (non-protein nitrogen), fraction Bl (rapidly degradable protein), fraction B2 (intermediately degradable protein), fraction B3 (slowly degradable protein) and fraction C (bound protein).