Blood chemistry and haematological parameters have been determined in the Antarctic teleosts, Notothenia neglecta Nybelin and Notothenia rossii Richardson at 2° C. Samples were taken using chronically implanted dorsal aortic cannulae following a minimum of 24–36 h recovery. Broadly similar results were obtained for the two species. In N. neglecta, routinely active specimens had high values of arterial pH (7.81) and PO2 (9.26 kPa), and modest haemoglobin levels (5.6 g dl−1) relative to temperate species. Following 3 min strenuous activity there was a decrease in arterial pH (7.63) and a small rise in lactate from 0.41 to 0.68 mm, but no significant change in the calculated net metabolic acid load (δHm+). PaO2 and PaCO2 varied inversely during exercise, and oxygen content declined by 22%. pHa and most other haematological parameters returned to routine values between 1–3 h post‐exercise. The results suggest that the major effect of strenuous activity in Notothenia spp. is a respiratory, rather than a metabolic acidosis.