The salivary elimination of ammonia and urea was studied in 4 permanently salivary duct fistulated sheep. Sheep were fed either a regular diet or the same diet with addition of non protein nitrogen (NPN). Individual saliva ammonia levels vary from 34 to 71 microgram N/100 ml. After intra-ruminal dosing with urea (10 g) or ammonia (2 g), the values may rise up to 1000 microgram N/100 ml. Saliva ammonia and blood ammonia changes follow the same direction. Daily saliva urea variations are correlated with feeding behaviour. NPN administration increases saliva urea and blood urea; both concentration curves are parallel.