Tumour necrosis factor-alpha (TNF-alpha) antagonist drugs have been associated with increased risk of tuberculosis (TB). Tuberculin skin test (TST) is the most frequently used tool for identification of latent TB infection. We herein aimed to analyse the effect of TNF-alpha antagonists on the TST responses in a prospective study. The study group consisted of 182 patients (99 female, 83 male) who received TNF-alpha antagonists for various rheumatic disorders. All patients were evaluated with TST along with other parameters on the day of referral and on the 12th month visit. For those patients with a response of < 5 mm induration at the initial evaluation, the TST was repeated to observe the booster effect. Out of 182 patients, 87 patients (48%) had a negative (0-4 mm) and 95 (52%) had a positive (a parts per thousand yen5 mm) TST response at initial evaluation. The TST responses were converted from negative at initial visit to positive at 1-year repeat in 26 (30%) patients. A significant increase was observed in the diameters of TST that were repeated on the first year of TNF-alpha antagonist treatment (9.15 +/- A 0.55) compared to their initial diameters (6.60 +/- A 0.51) (P < 0.001). Increased TST responses in patients receiving TNF-alpha antagonists may be associated with the restoration of suppressed immune reactivity against TB antigens with the decreased disease activity. The meaning of TST conversion in the definition of latent TB infection and the need for chemoprophylaxis in these patients remains to be answered by further studies.