This study was undertaken to determine the distribution of cat and dust mite allergens on wall surfaces and to assess the value of wall-wipe samples as a measure of allergen exposure. Paired samples were collected from 31 homes, 20 homes with cats and 11 homes without, by vacuuming 1 m2 of carpet and by wiping 1 square foot of an adjacent wall. Felis domesticus allergen I (Fel d I) was detected in 30 of 31 settled dust samples (range, not detectable to 832,000 mU/gm; median, 10,250 mU/gm) and in 27 of 31 wall-wipe samples (range, not detectable to 113.7 mU per filter; median, 1.2 mU per filter). There was a significant correlation between Fel d I content in settled dust and wall-wipe samples (rs = 0.73; p less than 0.001). To assess the reproducibility of the wall-wipe method, multiple wipe samples were obtained from 20 homes, revealing a mean coefficient of variation of 110%. In contrast to Fel d I, although Dermatophagoides farinae allergen I was detected in 23 of 25 settled dust samples (range, not detectable to 11,888 ng/gm; median, 1178 ng/gm), it was detected in only four of 25 wall-wipe samples. We conclude that cat allergen, but not dust mite allergen, is widely distributed on wall surfaces and that wipe samples provide a simple and effective means of assessing household exposure to cat allergen.