Aliphatic chlorinated hydrocarbons (ACHs) are widely used in several industrial processes and are also found in many commercial household products. They are classified as hazardous air pollutants, since ACHs exposure induces respiratory complications including airway hyperactivity. However, the contribution of airway smooth muscle tone to ACH-induced respiratory dysfunction has not been elucidated. Thus, the effects of ACHs such as dichloromethane (DCM), dichloroethane (DCE), and trichloromethane (TCM), on the basal and stimulant-induced contractile responses in piglet tracheal smooth muscle were investigated. ACHs at 100-1,000 ppm were found to evoke the basal contraction of tracheal smooth muscle strips. Although DCM, DCE, and TCM enhanced the muscle tone precontracted by KCl, they exerted differential effects on acetylcholine- or histamine-induced muscle contraction. DCE did not alter the muscle tone activated by acetylcholine and histamine. DCM at 1,000 ppm enhanced the muscle tension precontracted by acetylcholine but not by histamine. TCM at 30-1,000 ppm increased the histamine-induced muscle contraction, but at 1,000 ppm relaxed the muscle precontracted by acetylcholine. DCE and TCM at the highest concentration (1,000 ppm) provoked a biphasic response with an initial increase in KCI-induced muscle tension followed by a decrease. Furthermore, pretreatment with DCE potentiated the acetylcholine-, histamine-, and KCl-induced muscle contractile responses. Pretreatment with TCM potentiated the histamine-, and KCl-induced response, but DCM only potentiated the KCl-induced response. The results suggest that ACH exposure altering the basal and spasmogen-induced contractile responses might participate in airway impairment with hyperresponsiveness.