The prevalence of active tuberculosis and positive tuberculin skin tests was assessed in 132 corticosteroid-treated asthmatics for an evaluation period that represented 620 corticosteroid-years of therapy. There was no evidence of active tuberculosis in any of these patients. Positive intermediate-strength tuberculin tests were present in 28% of patients and correlated with increased age. In patients treated with daily corticosteroids, tuberculin negativity was associated with a higher dose of corticosteroids. Positive second-strength tuberculin tests were found in 42.3% of the patients with negative intermediate-strength tests and also correlated with increased age. Based on these data as well as the prevalence of significant liver disease in older patients receiving isoniazid (INH), routine INH chemoprophylaxis for corticosteroid-treated asthmatic patients, regardless of their tuberculin cutaneous reactivity, is not indicated.