The relationship between oral temperature and other parameters of illness was examined in 51 adult volunteers who were inoculated experimentally with partially attenuated candidate dengue virus vaccines. In subjects who developed clinical illness, the peak illness temperature, mean illness temperature, and peak 6:00 A.M. illness temperature all correlated positively with the total number of signs and symptoms other than fever and with a fall in the white blood cell count (the latter was the only laboratory abnormality significantly associated with clinical illness [P = .02]). Of these factors, the peak 6:00 A.M. oral temperature exhibited the strongest correlations with the two parameters used to estimate severity of illness (rxy = .58 and P < .01 for signs and symptoms; rxy = .37 and P = .01 for fall in white blood cell count).