The recognition of children with tuberculous infection without disease is often difficult. Minimal active disease may be present in many cases but unrecognised on chest radiography or by microbiologic methods. We have performed computed tomography in 22 children with tuberculous infection, a normal chest radiograph and negative microbacterial culture. In 16 children we also performed DNA amplification by polymerase chain reaction in gastric aspirates. It was found that 14 of 22 (63%) infected children had enlarged lymph nodes. Adenopathies were more frequent in children less than 8 years-old and in the right paratracheal positions. Polymerase chain reaction was positive in 4 of 8 studied children with abnormal computed tomography and in none of the children with normal computed tomography. The demonstration of unrecognised active disease raises the question of the adequate treatment for the children with tuberculous infection. It is proposed that a two drug regimen would be more appropriate than isoniazid alone in children less than 8 years old.