A pulmonary tumorous shadow appeared and enlarged in a 25 years-old male patient undergoing intensive chemotherapy for tuberculosis. The chest X-rays taken on admission revealed effused pleura in the right lung and nodular shadows in the upper area of the right lung. After 40 days of using isoniazid (INH), rifampicin (RFP) and streptomycin (SM), a homogeneous opacity, not previously observed, appeared in the middle area of the right lung (S5). Microscopic examination of the tissues obtained during a transbronchial lung biopsy disclosed epithelioid cell granulomas with marked eosinophilic infiltration. The presence of eosinophilic infiltration due to the admission of antituberculosis agents was disregarded because no change was observed in the new granulomatous shadows during the drug challenge tests and the lymphocyte stimulation test to INH, RFP and SM was negative. Transient aggravation during the initial phase of chemotherapy for pulmonary tuberculosis, such as in this case, is suspected cause by some eosinophilic allergic-induced mechanisms, against bacillary components.