The course of fever was examined in 75 patients with pulmonary tuberculosis treated with modern chemotherapy. Sixteen patients (21%) were afebrile and differed from 59 febrile patients (79%) by having lower incidences of the following: symptoms (p < 0.02), alcoholism (p < 0.01), lung cavitation (p < 0.01), "far advanced disease" (p < 0.05), and sputum smears containing "numerous" acid-fast bacilli (p < 0.01). Resolution of fever was variable (mean, 16 days; median, 10 days; range, 1 to 109 days). Thirty-eight patients (64%) became afebrile within 2 wk (group 1); 21 (36%) had fever for longer than 2 wk (group 2). Far advanced disease and high temperature (> 38.8 degrees C) on admission were more frequent in group 2 (p < 0.05 and p < 0.01, respectively). However, the groups did not differ in demographic features or in the frequency of symptoms on admission, alcoholism, lung cavitation, numerous acid-fast bacilli on sputum smears, or coexisting bacterial respiratory infection. Antimicrobial drug treatment of presumed coexistent bacterial infection in 19 febrile patients did not influence the course of fever. Analysis of variance and covariance were used to compare the independent effects of various antituberculosis drug regimens on the course of fever; no significant differences were observed.