Learning ObjectivesRecall the findings of past studies of lower respiratory function in persons having multiple chemical sensitivity (MCS).Identify criteria for participating in the present study, the grounds for exclusion, and how the trial was carried out.Explain the ways in which patients diagnosed as having MCS differed from control subjects in their reactions to inhaled capsaicin, and the possible implications of these findings.Multiple chemical sensitivity (MCS) is characterized by chemically induced symptoms from multiple organ systems. No consistent physical findings or laboratory abnormalities have been determined for the associated symptoms. Twelve patients with chemically induced airway symptoms, who satisfied Cullen’s criteria for MCS, were provoked double-blind, randomized with saline and three increments of inhaled capsaicin. The recordings were compared with those of a control group of healthy individuals. The results found that the patients coughed more than the control subjects at each dose of capsaicin (P < 0.05 for 0.4 &mgr;mol/L capsaicin and P < 0.005 for 2 &mgr;mol/L and 10 &mgr;mol/L). The capsaicin provocation also induced significantly more symptoms in patients with MCS. We conclude that airway sensory reactivity is increased in patients with MCS, a finding which suggests that neurogenic factors may be of importance in this condition.