Haemodynamic responses to hypothermia were studied at normal haematocrit and following the induction of acute normovolaemic haemodilution. Experiments were performed on 20 cats anaesthetized with a mixture of chloralose and urethane in two groups. In one group (n = 10) the effects of hypothermia on various haemodynamic variables were studied at normal haematocrit (41.0 +/- 1.7%) and in the second group of cats (n = 10) the effects of hypothermia on various haemodynamic variables were studied after the induction of acute normovolaemic haemodilution (14.0 +/- 1.0%). The haemodynamic variables left ventricular pressure, left ventricular contractility, arterial blood pressure, heart rate and right atrial pressure were recorded on a polygraph. Cardiac output was measured using a cardiac output computer. In both groups hypothermia was induced by surface cooling with the help of ice. Cardiovascular variables were recorded at each 1 degree C fall in body temperature. Hypothermia produced a significant (P < 0.05) drop in heart rate, cardiac output, arterial blood pressure and left ventricular contractility in both groups. However, the percentage decrease in these variables in response to hypothermia was significantly (P < 0.05) higher in cats with low haematocrit than in those with normal haematocrit. The severity of hypothermia--induced cardiovascular effects is evident from the drastic decrease in heart rate, cardiac output, arterial blood pressure and myocardial contractility in cats with low haematocrit, indicating a higher risk of circulatory failure under anaemic conditions at low temperatures.