A three-dimensional time-dependent magnetohydrodynamic (MHD) simulation was used to model the interaction between the solar wind and the plasmas produced from cometary gases. The model, which includes cometary mass loading, reproduced several features observed by the recent missions to comet Halley: (1) a weak bow shock was formed 3.2¿105 km in front of the comet, (2) the magnetic field increased by a factor of 3.7 across this weak bow shock and continued to increase up to the contact surface (Bmax/BIMF=~6--8), and (3) the plasma temperature increased across the bow shock but decreased nearer to the comet. In addition, interplanetary magnetic field (IMF) lines were hung up on the comet and formed a long tail in which the lobe magnetic field was quite strong (Blobe/BIMF~5). A cold dense plasma sheet oriented normal to the IMF direction formed in the tail. ¿ American Geophysical Union 1988