This study was conducted at Basic Medical Sciences Institute (BMSI) Karachi in the year 1998. Antigen induced histamine released from sensitized lung parenchymal tissues was observed within the initial 15% of the duration of contraction, responsible for the initial phase contraction and protracted phase were mediated by the release of other autacoids from sensitized mast cells. Ovalbumin sensitized guinea pigs lung parenchymal tissue was exposed to specific antigen in vitro, resulted in a rapidly developing, prolonged contraction. Treatment of the tissue with sodium cromoglycate before antigen exposure inhibited or delayed the onset and decreased the amplitude of contraction the response was dose dependent. The data suggested that sodium glycate treatment of the tissues prior to antigen exposure stabilizes the mast cell membrane with the resultant inhibition of mast cell disruption and release of chemical mediators that are responsible for the early and late phase contraction. Sodium cromoglycate in concentration of 106 g/m (1?g/ml) completely antagonizes the antigen induce contraction.