Twelve alcoholic extracts and 12 hexane extracts of plant materials selected on the basis of medicinal folklore for asthma treatment in Indonesia were studied for their activity in inhibiting histamine release from RBL-2H3 cells (rat basophilic leukemia cell line), a tumor analog of mast cells. The results of screening indicated that five alcoholic extracts (Plantago major leaves, Eucalyptus globulus leaves and fruit, Cinnamomum massoiae cortex, Vitex trifolia leaves) and two hexane extracts (Eucalyptus globulus leaves, Vitex trifolia leaves) inhibited IgE-dependent histamine release from RBL-2H3 cells. The inhibitory effects were found to be more than 80% for extract concentrations of 0.5 mg/ml. The results indicate that the extracts contain active compounds that inhibit mast-cell degranulation, and provide insight into the development of new drugs for treating asthma and/or allergic disease.