-2,2-dimethylpropanesulfonam ide (6) showed excellent anti-asthmatic activity and the longest duration of action. The compounds bearing a methyl group at the 7 or 8 position of the imidazo[1,2-b]pyridazine ring were found to have enhanced activity. Among them, 3-(7-methylimidazo[1,2-b]pyridazin-6-yl)oxy-2,2- dimethylpropanesulfonamide (25) showed the most potent inhibitory effect, and its anti-asthmatic