Two patients with rheumatoid arthritis (RA) that developed serious infectious complications following anti-TNFalpha therapy (infliximab) are reported. Patient 1 developed tuberculosis with high fever, refractory diarrhea and mediastinal lymphadenopathy. Trans-bronchial needle biopsy was useful to confirm the diagnosis. Patient 2 showed sudden onset of dyspnea with diffuse bilateral lung infiltration caused by pneumocystis jiroveci pneumonia and the diagnosis was confirmed by broncho-alveolar lavage. Physicians should be alerted to infectious complications with atypical presentation and rapid progression in infliximab-treated patients. Invasive diagnostic procedures including fiber-optic bronchoscopy may be necessary early in the course for such cases.