Ten patients were included in a double-blind crossover trial, designed to compare the effects of a new anti-asthmatic agent Minocromil, an organic decarboxylic acid, and placebo on bronchial allergen challenge. The challenges were performed at weekly intervals. Significant differences in favour of Minocromil were found in the concentration of antigen reached at which FEV1 fell below 20% of baseline. This was confirmed by analysis of the decrease in FEV1 recorded at the highest concentrations of antigens, which showed statistically significant differences in favour of Minocromil.