Abstract 1. 1. The whole-blood oxygen equilibrium curve in carpet sharks ( Cephaloscyllium isabella) at 15°C is weakly cooperative (Hill's coefficient n = 1.5) with a moderate Bohr effect (Δlog P 50 Δ pH = −0.32 ) and high O 2 affinity ( P 50 = 8.3 mmHg at pH 7.7). 2. 2. Warm acclimated sharks (15°C) did not alter the erythrocytic trinucleotide concentration but had high urea levels which increased O 2 affinity by comparison with sharks acclimated at 5°C. 3. 3. ATP decreased the O 2 affinity of “stripped” Hb solutions whereas urea increased it. Equimolar concentrations of both cofactors suggested suppression of the phosphate effect by urea. 4. 4. Blood from embryonic carpet sharks (12–15 mm long) showed similar O 2 affinities to blood from adult sharks.