Objective: The purpose of this study was to identify values for net acid base excretion (NABE) which are significant indicators of the acid-base equilibrium in pregnant and young ewes and to show its relationship with other parameters (base, acid, ammonium [NH(4)], base-acid quotient, sodium [Na], potassium [K], calcium [Ca]) in ovine urine. In contrast to dairy cows, data are rare on these parameters in ewes. Material and methods: A total of 99 animals were used in the study, consisting of 56 young (average of 5.6 +/- 1.1 months) and 43 pregnant ewes (average of 35.2 +/- 18.8 months). Measurement of fractional NABE in urine samples was carried out according to the method reported by Kutas. The pH value of the urine was measured with a laboratory pH meter. Na, K and total Ca were measured with a flame photometer. Results: For all values except Na significant differences occurred between urine samples of pregnant ewes and young ewes (p < 0.001). Base, acid, NH(4), NABE, K and Ca values were significantly higher in the urine of the youngs than in pregnant ewes. In young ewes, a strong correlation was found between NABE and base values while a weak correlation could be observed between pH and base values. In pregnant ewes, strong NABE-base, NABE-K, K-acid and K-base correlations were found as well as weak NH(4)-base, NH(4)-NABE and NH(4)-K correlations. There was a strongly positive correlation between NABE and NH(4) in pregnant ewes, while a weak negative correlation between those values was observed in young ewes. Conclusion: For the first time, we established values for NABE and certain other parameters in urine of pregnant ewes and young ewes. It was shown that the acid-base balance in pregnant ewes and young ewes can be evaluated by measuring NABE and certain trace elements in urine like in cattle.