NEW YORK, June 14 (Praxis Press) Despite improvements in tuberculosis (TB) control during the past decade, Mycobacterium tuberculosis transmission continues to occur in the United States. Chin and colleagues examined 221 TB case-patients in the San Francisco Bay area and found that seventy-three resulted from one strain of M tuberculosis. Thirty-nine of the 73 case-patients developed TB because they were not identified as contacts of source case-patients; 20 case-patients developed TB because of delayed diagnosis of their sources; 13 case-patients developed TB because of problems associated with the evaluation or treatment of contacts; and 1 case-patient developed TB because of delay in being elicited as a contact (see paper). Reasons for TB transmission include failure to identify contacts of source case-patients, delayed diagnosis of source case-patients, and problems associated with evaluation or treatment of contacts.