The mean plasma ionized calcium in 35 normal lactating ewes was 4,25 ±0,49 mg/l00 ml (1,06 ±0,12 mM/l) and in 26 normal single 21-28 day old suckling lambs was 4,47 ±0,65 mg/100 ml (1,12 ± 0,16 Mm/1). On average this constituted 41,29 ±4,44%of total calcium in ewes and 41,69 ± 5 ,69%in lambs. Although there was a significant correlation between ionized calcium and total calcium in both ewes (P < 0,05; r =0,416) and lambs (P < 0,05; r =0,417) this was not of a sufficiently high order to predict ionized calcium from total calcium levels. In ewes there was a significant negative correlation between total calcium and inorganic phosphate (P < 0,05; r = -0,388), a highly significant negative correlation between ionized calcium and inorganic phosphate (P < 0,01; r = 0,625) and a highly significant positive correlation between total calcium and magnesium (P <0,01; r = 0,442). Similar correlations were not found in lambs. In both ewes and lambs no relationship was found between total calcium, ionized calcium or the ration between the two and plasma protein.