A model of Saturn's magnetospheric magnetic field is obtained from the Voyager 1 and 2 observations. A representation consisting of the Z3 zonal harmonic model of Saturn's planetary magnetic field together with an explicit model of the equatorial ring current fits the observations well within r<20 RS, with the exception of data obtained during the Voyager 2 inbound pass. The exception is attributed to a time variation of Saturn's magnetosphere driven by a drop in solar wind ram pressure. The magnetohydrodynamic momentum equation isused to obtain, from the magnetic field model, estimates of the plasma pressure and mass density at radial distances of 8<r<16 RS. These estimates are generally consistent with those obtained by the Pioneer 11 and Voyager plasma investigations. The Voyager 1 observations suggest the presence of a global field-aligned current of ~107 A flowing into the (southern) auroral zone in the evening sector. No evidence of such a field-aligned current system is found in the Voyager 2 observations obtained a year later.