An accidental discharge of a Halon 1301 system is reported. Thirty-one workers were assessed, 22 who were present at the time of the discharge, and 9 who worked the next shift. The incident was complicated by a small Freon-22 leak several hours later. Throat, eye, and nasal irritation and lightheadedness were reported by the majority of workers. Workers present during the halon discharge reported significantly more lightheadedness, headache, voice change, cough, and a fast heartbeat than did those who worked the later shift. These differences were significant even after correcting for confounding factors such as age, sex, and sense of anxiety at the time of the incident. The possible causes for the irritant symptoms include breakdown products of Halon 1301 and Freon-22 or contaminants from the halon discharge system. Although these irritant effects may not be an effect of Halon 1301 alone, they may occur in these discharge situations, and workers should be advised of this possibility. The possible cardiac and central nervous system effects also should be considered. The importance of a clear-cut protocol to deal with such incidents as well as worker education are discussed.