To assess the influence of halothane anaesthesia on the distribution of blood volume in supine humans, we used albumin labelled with 99mTc to measure blood volume distribution along the craniocaudal axis. We studied 6 volunteers in the supine position before, during and after anaesthesia with 1% halothane and 66% nitrous oxide. Using collimated detectors above and below the subject, counts were obtained from the legs, pelvis, abdomen, rib cage and head, with the arms excluded. During anaesthesia, the proportion of counts detected in the legs increased, but failed to achieve significance (P = 0.059). On recovery from anaesthesia, leg counts decreased significantly. Counts in the abdomen and rib cage decreased significantly during anaesthesia and the abdomen counts increased again on recovery (P = 0.036 for all changes). These results confirm other studies of the vascular effects of halothane, and do not support the hypothesis that blood volume redistributes from the legs to within the chest wall during anaesthesia.