The spatial and temporal characteristics of blood flow in the normal adult human carotid bifurcation are investigated by two different methods: in vitro pulsatile flow model experiments using laser Doppler anemometry and in vivo studies employing pulsed Doppler velocity measurements obtained with an ultrasound duplex scanner. Glass and Plexiglas models based upon arteriographic measurements were evaluated with laser Doppler anemometer methods for pulsatile flow. A similarity approach permits the model study to be geometrically and hydrodynamically accurate with respect to the human carotid bifurcation. These parallel but separate approaches were originally performed by the principal authors without knowledge of each others' work. Normal flow patterns in the proximal internal carotid artery are demonstrated to include: unidirectional, helical, transient reversal, and low velocity regions of flows. The characterization of these complex temporal and spatially variant flow fields required the high sample volume resolution afforded by the model study. Pulsed Doppler ultrasound and a novel method of positioning the sample volume permitted a qualitative description of the complex flow velocity fields in the normal human bifurcation. Results of the two methods are compared and a striking similarity between the two methods is observed for the primary and secondary flow features. The problem of associating blood flow velocity disturbances with the presence of intralumenal disease is addressed in the discussion. It is suggested that the flow disturbances associated with the normal carotid bifurcation are different from those associated with intraluminal disease and further, that the secondary flow structures can be usefully employed to establish normalcy.