Disodium Cromoglycate (Lomudal) was developed from a natural product, Khellin, which has been used clinically since ancient times for the treatment of colics. In contrast to Khellin Lomudal possesses few pharmacological properties; it has a low order of toxicity and is rapidly excreted unchanged from the body. It does not antagonise any of the known spasmogens e.g. histamine or SRS-A, etc.; neither does it have any bronchodilator or anti-inflammatory activity. In man when it is administered by inhalation prior to antigen challenge it inhibits the bronchospasm induced by the antigen. However, it has little or no effect if given after antigen challenge. When inhaled immediately before antigen challenge the maximum protective effect was achieved by extremely small doses (of the order of 0.1 mg). If the time interval between drug inhalation and antigen challenge was extended, much larger doses (several mg) were necessary to maintain its effect. Thus it is the duration of action rather than degree of immediate protection which is dose dependant. In clinical practice 20 mg inhaled four times a day will maintain a high level of protection over a 24-hour period. In sensitised rats the compound selectively supresses certain specific immunological reactions, e.g. PCA induced by reaginic type antibody-antigen interaction. In these reactions it inhibits mast cell disruption as well as preventing the release of chemical mediators. Recent clinical and laboratory evidence suggests that the drug may be less specific in its action than was originally inferred. For example in the laboratory it has been shown to inhibit immunological reactions involving precipitating antibodies as well as mast cell degranulation induced by Phospholipase A. In clinical practice Lomudal has been demonstrated to prevent bronchospasm mediated by non-reaginic antibodies. Furthermore it will inhibit at least partially the post exercise fall in FEV1 in children and adults. Evidence is also presented which suggests that although Lomudal has a number of apparently distinct pharmacological actions it is still possible to visualise a single mode of action of this drug at the cellular level.