Temperature is an environmental factor which has profound effects on both aerobic and anaerobic activities. During aerobic activity, hydrogen ions from acidic metabolites are consumed by oxidative phosphorylation. When anaerobic burst of activity occur, hydrogen ions must be buffered to prevent an excessive fall in pH which might inhibit normal physiological processes. Temperature alters the ... protonation state of many compounds and thus a key feature of intracellular buffering requires that protonation should be preserved over a range of temperatures. White skeletal muscle, red muscle, ventrical muscle from the hearts and blood was obtained from the Antarctic fish Dissostichus mawsoni, Pagothenia borchgrevinki, Trematomus centronotus, P. macropterus and Rhigophila dearborni and in vitro muscle buffering capacity was estimated for each muscle type. Blood hemoglobin concentration was determined optically and related to blood buffering capacity.