An outbreak of Kawasaki syndrome occurred in eastern Colorado during April and May, 1982. 48% of 23 cases had been exposed to the application of rug shampoo in the home in the 30 days before onset of disease, compared with 10% of 30 matched neighbourhood controls and 11% of 56 randomly chosen, matched community controls (p<0·01). The interval between rug shampooing and onset of disease was 16-25 days in 9 of 11 cases; 4 of the 9 had intervals of exactly 20 days. Although many brands of shampoo and three different methods of application were used, all but 1 of the cases had walked or crawled on the shampooed rugs within 2 h, the interval being significantly longer for those controls who had been exposed to the shampoo. 3 of 5 sporadic cases in Colorado who fell ill after November, 1981, had similar histories of exposure, as did 9 of 15 sporadic cases in eight other states who were contacted after the Colorado investigation. These findings suggest that exposure to the application of rug shampoo may be a risk factor for some cases of Kawasaki syndrome, although the mechanism remains to be determined.