When used to restrain rats while obtaining cardiac blood, there was little difference between the effects of ether, pentobarbitone sodium, and fentanyl plus droperidol on acid-base balance, haemoglobin, haematocrit, plasma protein, calcium and magnesium. The use of manual restraint increased blood acidity, plasma protein, calcium and magnesium, but decreased blood glucose. Haemoglobin and haematocrit values were higher for tail blood than for blood removed from the heart or abdominal aorta.