Two cases of hypersensitivity reaction to antituberculosis drugs are reported. With streptomycin and para-amino salicylic acid, one presented spiking fever, generalized erythematous dermatitis, lymphadenopathy, hepatitis with icterus, and a blood picture resembling infectious mononucleosis with leukemoid-lymphocytic reaction. Following desensitizing doses of streptomycin and PAS, the patient again showed evidence of toxicity to these drugs and also apparent cross-reaction with viomycin. He tolerated isoniazid, pyrazinamide, and the broad-spectrum antibiotics. The other with PAS, isoniazid and chlorpromazine developed granulocytopenia, pleuropneumonia, and rapidly progressive circulatory failure attributed to bacterial toxemia, with no response to combined broad-spectrum antibiotics. The responsible drug or drugs could not be determined because of the rapidly fatal termination 26 hours after the onset of the acute illness. Preliminary clinical observation does not specifically implicate one single or combination of drugs. Our clinical experience in the evaluation of the supplemental use of vitamins in correcting clinically suspected deficiencies has been favorable when a drug suspected of causing toxicity was resumed and apparently well tolerated.