The effect of isovolemic hemodilution using dextran-60 on arterial blood flow in the rabbit ear was investigated. The animals were anesthetized and an electromagnetic flow probe was applied around the central artery of the ear. Isovolemic hemodilution was performed during a 15 min exchange period. Two degrees of hemodilution were investigated [8.5 and 17 ml dextran-60/kg body weight (b.w.)] and compared with a nontreated control group. The two levels of hemodilution induced reductions in hematocrit to 29 and 21%, respectively, from the control level of about 40%. In all groups, blood pressure maintained constant levels throughout each experiment, which lasted 240 min. In the controls, ear artery blood flow was unchanged or decreased slightly during the experiment. The lower level of hemodilution caused a slight increase of blood flow after 4 h. In the group treated with 17 ml/kg b.w. dextran, blood flow gradually increased after 90 min following hemodilution. After 240 min, flow rates had increased to two- or threefold the initial rate in this group. Although other possibilities exist, the increased blood flow following hemodilution may be interpreted as reflecting a decreased resistance to flow in the tissue due to the decreased viscosity of the blood.