Of 38 cases of uveitis examined from 1970 to 1980 in which a tuberculous cause was considered, we classified 18 as presumed tuberculous on the basis of a positive response to isoniazid. We compared these patients to a control group who had a positive skin test but a negative response to the isoniazid therapeutic test. We found a family history of tuberculosis in seven of the 18 (P less than .05) and a more common (18 of 36 eyes) incidence of iridocyclitis (P less than .05) than of other types of uveitis. A uveitis patient who has a positive tuberculin skin test of any size or strength should undergo the isoniazid therapeutic test to ensure that a possible diagnosis of tuberculous uveitis is not missed. Tuberculosis should be suspected in both granulomatous and non granulomatous uveal lesions, especially in cases of chronic iridocyclitis.