Of 75 patients with sarcoidosis observed during their initial hospitalization for diagnostic purposes, 41% exhibited fever of significant magnitude and duration. Often this was accompanied by night sweats, chills and/or leukocytosis. The occurrence of fever could not be correlated with the age or sex of these patients or with the extent, localization or activity of their underlying sarcoidosis. Although the duration of symptoms was somewhat shorter in those with fever, there were many exceptions, so that fever was not necessarily an early manifestation of the disease. Negroes exhibited fever significantly more frequently than white patients, suggesting that host factors may have been involved in the febrile response to sarcoidosis. Failure to recognize that sarcoidosis may give rise to fever was responsible for many diagnostic errors and often led to futile therapeutic trials with specific agents directed against tuberculosis and other infections, and to unnecessary prolongation of hospitalization.