It is generally recognized that cat skin is an important extrasalivary source of the major cat allergen, Fel d I. Nevertheless, since cat saliva is readily applied to the skin during grooming, we tried to demonstrate that Fel d I can accumulate on cat skin without licking. Eight adult female cats were used. On day 0, two separate sites of the trunk were shaved and a 6 cm2 area in each site was washed three times with 5 ml of distilled water. The first and third washes were collected and stored for assay. The areas were then covered with an occlusive dressing. Twenty-four hours later, the site was washed once and the sample stored. On day 7, washes were collected as on day 0, and a collar was attached to the neck to prevent contamination from saliva. A single wash was done 24 hours later. Comparison of data was achieved with an analysis of variance. Repeated washes significantly reduced Fel d I levels from 35 +/- 21 to 10 +/- 9 mU/cm2 on day 0 (p less than 0.01) and from 36 +/- 18 to 12 +/- 7 mU/cm2 on day 7 (p less than 0.01). Fel d I levels increased significantly after 24 hours of occlusion from 10 +/- 9 to 41 +/- 24 mU/cm2 (p less than 0.01) and collar wearing from 12 +/- 7 to 54 +/- 21 mU/cm2 (p less than 0.001). These findings demonstrate that Fel d I is produced by cat skin. Mean daily production of Fel d I by cat skin is estimated to be 36 units. Cat skin is an important extrasalivary source of Fel d I.