A harmless magnetic field produced by an extracorporeal magnet induces in the blood vessels of a living subject electrical signals which carry information about regional blood flows. Loop probes of hairlike consistency equipped with fine electrodes can now be introduced percutaneously and selectively into the vasculature through angiographic catheters to pick up these magnetically induced signals at selected loci. In addition to a continuous record of phasic blood flow, the loop sensors provide signals which measure variations in vascular diameters, thus yielding a continuous record of active and passive vasomotion. Coupled with blood pressure recordings, these data will permit determination of the elastic constants of blood vessels in situ. The manifold capabilities of electromagnetic rheoangiometry for providing continuous records of these vascular parameters are illustrated in dogs with tracings using multichannel recorders which provide continuous information of arterial blood pressures, instantaneous and mean blood flows, and instantaneous and mean vascular diameter changes simultaneously in two nonadjacent arteries.