Nedocromil sodium (and sodium cromoglycate) are topical, prophylactic, anti-inflammatory agents used in reversible obstructive airways disease. To investigate their potential mode of action, the effects of these agents on specific allergen- or IL- 2- induced proliferation of a human CD4+ house dust mite-specific T-cell clone isolated from an individual with perennial rhinitis was examined. Although strong proliferation was observed in control cultures, no inhibitory effect was observed with any of the drug concentrations tested. In contrast, dexamethasone was able to inhibit the T-cell proliferation. These observations suggest that the clinically observed suppression of the late-phase asthmatic response may not be due to an effect on CD4+ T lymphocytes.