Pioneer Venus observed the hydrogen coma of Comet P/Giacobini-Zinner on 11 September 1985 during the ICE fly-by. Analysis of these data with a time-dependent 3-D particle-trajectory model implies a water production rate of 2.2¿d1028 s-1 on that day. The model includes the irregular varications in the H lifetime from simultaneous measurements of the solar wind by ICE and of the solar UV by SME, respectively. The H lifetime varied from 2¿105 to 3¿106 s during the 42 days preceding the observation.