VEGA‐1 measurements of the plasma density and magnetic field in the coma of Comet Halley show characteristic signatures over a significant portion of the outbound pass. It is found that the assumption that there is a balance between the thermal and magnetic pressures in these features can be used to obtain estimates of the plasma temperature as a function of distance from the nucleus. These estimates indicate that the ions cool from ∼1.5 × 106°K at 105km to 2 × 105°K at 5 × 104km. The technique used here represents a novel approach whereby temperature measurements can be made in situations where only plasma density and magnetic field data are a