Hypocalcaemia was verified in 74.4% of 78 ewes with a clinical diagnosis of hypocalcaemia, the corresponding figure for 99 ewes with an uncertain clinical diagnosis of hypocalcaemia being 21.2%. The tendency to developed hypocalcaemia increased with increasing age. Hypocalcaemic cases were recorded from about 2 months prior to lambing to approx. 11/2 months after lambing, most frequently occurring during the period 2-4 weeks before lambing. The number of lambs in ewes which developed hypocalcaemia was on the average greater than in a group of healthy control ewes. Plasma Ca was higher in ewes with hypocalcaemia which stood firmly as compared with atactic or recumbent cases, and higher in those which showed tetany, were restless or which appeared to be relatively normal, than in those which were dull or comatose. Plasma Mg was lowest in the ewes with tetany. Values for ASAT, ALAT, bilirubin, haemoglobin and packed cell volume were significantly higher in hypocalcaemic ewes than in the healthy control ewes. In the hypocalcaemic ewes, plasma Ca and packed cell volume were negatively correlated, while plasma Ca and plasma P were positively correlated. Approx. 20% of the ewes with hypocalcaemia did not recover. These had higher average plasma Ca and lower average plasma Mg at first treatment than those which recovered. The mortality rate in ewes treated after parturition was higher than in those treated before parturition. Of the hypocalcaemic cases which recovered, approx. 25% required more than one treatment. Ewes which developed hypocalcaemia before lambing and which recovered, lost 22% of their lambs, the main reason probably being premature birth. The differential diagnosis of hypocalcaemia is discussed in the light of clinical and clinico-chemical findings in normocalcaemic ewes to which a diagnosis of clinical or uncertain clinical hypocalcaemia had been given.