A spherical harmonic model of Jupiter's planetary magnetic field is combined with a self-consistent model of the Jovian magnetodisc. The sets of parameters of both models are determined simultaneously by using a generalized inverse technique. Assuming that the pressure P in the middle (and outer) magnetosphere is related to the unit flux tube volume V through PV&ggr;=const, the fit yields a value of 0.88 for &ggr;. If the hot (30 keV) plasma is transported adiabatically inward under the interchange instability triggered by the centrifugal force of the heavy torus ions, losses are not sufficient to account for such a low value of &ggr; beyond L=10 (as compared to &ggr;≈5/3 that would be expected for adiabatic transport of monoatomic gas). Closer to the planet, as the outer edge of the Io plasma torus is approached (at distances between 7 and 9 RJ from Jupiter), PV&ggr; is found to decrease inward, as expected from the particle measurements, which identified an inner boundary of the particle fluxes in that region. At the magnetic equator, our pressure estimates were compared with the ones obtained from direct particle measurements (low-energy charged particle (LECP) experiment). Assuming a mixture of O+ and H+ at the same temperature (or with the same spectral power law exponent), consistency between those two independent determinations of the pressure would require that the pressure produced by H+ constitute 18--36% (at most) of the total pressure, at distances between 13 and 21 RJ. Finally, as concerns the internal field coefficients, despite an overall consistency, a slight variability is found between the present estimates and previous ones derived from the same data set, which puts some limitation on the accuracy with which internal coefficients can be determined from the Voyager 1 encounter alone. ¿ American Geophysical Union 1989