The plasma velocity in the magnetosphere of comet Halley is calculated by using the displacement of magnetic field lines during the Giotto flyby. The obtained profile is in good agreement with that found from the momentum balance condition. The radial component of plasma velocity measured in situ (Schwenn et al., 1987) correlates well with the spacecraft position in the coordinate system rotating with the interplanetary magnetic field. The radial velocity is shown to be larger in the plane perpendicular to the interplanetary magnetic field (IMF) than in the plane containing the IMF vector. The transverse (to the Giotto trajectory) velocity component decreases toward the nucleus, almost vanishing at the Halley ionopause. This fact favours our previous conclusion (Israelevich et al., 1992) that the conventionally used values of the gas production rate and/or ion-neutral momentum exchange rate require reexamination. We arrived at the conclusion that the plasma dynamics in the comet Halley magnetosphere can be fairly well described by the frozen-in magnetic field approximation; that is, the magnetic Reynolds number in the cometary ionosphere is high. ¿ American Geophysical Union 1995.