Recent events in the Middle East have made the study of the negotiations of the Chemical Weapons Convention a matter of urgency. The negotiations have addressed verification of compliance with those provisions of the Convention which relate to the production and non-production of relevant chemicals. In order to facilitate the work of the negotiators, the Pugwash movement and SIPRI gave a group of scientific and other experts on the negotiations the task of analyzing how the current Convention provisions should be applied to the specific chemical, thiodiglycol, a precursor to mustard gas. The authors present their findings and include outlines of particular problems of monitoring thiodiglycol production, which can be used as a model for the monitoring of other chemicals to be covered by the Convention in the future.