Studies conducted during the first world war reported the first evidence for a skin reservoir of sulphur mustard (HD). Further work, from the same period, concluded that this apparent reservoir could be removed by solvent up to 45 minutes post exposure. The existence of a skin reservoir was subsequently refuted in a number of studies conducted during the second world war. Since this time it has become widely accepted that HD rapidly penetrates the skin and becomes “fixed” by reacting with skin constituents such as proteins. Contemporary studies have noted the presence of “free” HD or its metabolites in isolated, perfused, porcine skin flaps. Most recently, a study investigating the in vitro skin absorption, distribution and non-enzymatic hydroysis of HD, has demonstrated a large (up to 36% of the applied dose) reservoir of HD present for at least 24 hours post exposure. Clearly, these studies contrast with data generated during World War II. It is important that the putative existence of a HD skin reservoir is substantiated, as this may potentially have significant implications for personnel decontamination and the safety of emergency medical personnel. The purpose of this paper is to outline a proposed study to investigate the existence of such a depot. Preliminary experiments will investigate the putative reservoir in both human and pig skin in vitro and, if present, quantify it in terms of amount of agent and persistence. Further studies will seek to establish the kinetics of HD absorption through different skin layers in order to identify the precise location of the reservoir.