We evaluated 191 consecutive adults with pulmonary tuberculosis in order to develop methods to determine which patients should be initially hospitalized. Using stepwise discriminant analysis, we found the six factors that were most strongly associated with an unfavorable short-term outcome (respiratory failure or death): lymphopenia, advanced age, concomitant smear-positive extrapulmonary tuberculosis, alcoholism, a high percentage of neutrophilson the differential white blood cell count, and lack of radiographic evidence of cavitation. We derived a scoring system incorporating these variables and separated patients into high- and low-risk groups. The system was prospectively validated by applying it to a separate group of 179 patients. Lymphocyte-transformation tests in 32 patients revealed an association between clinical markers of poor prognosis and minimal lymphocyte proliferation to a heat-killed strain of Mycobacterium tuberculosis.