Among 244 patients aged 18 to 98 years who were consecutively hospitalized in a department of internal medicine because of a febrile disease, 52 (21%) were bacteremic. On a logistic regression analysis, five variables known within 24 hours of admission were found to be associated both significantly and independently with bacteremia: low serum albumin level, low premorbid performance status, chills, renal failure, and an assumptive diagnosis of urinary tract infection on admission. The logistic model was used to divide patients into three groups. In group 1, the percentage of bacteremic patients was 5%, in group 2, 40%, and in group 3, 83%. The percentage of deaths in the three groups was 0%, 23%, and 50%, respectively. The model was validated in a second group of 257 patients. The percentage of bacteremia was 1% in group 1, 23% in group 2, and 65% in group 3. The death rate in three groups was 3%, 4%, and 35%, respectively. The accuracy of the attending physician in diagnosing bacteremia within 24 hours of hospitalization was compared with that of the model. Use of the model could have improved the diagnostic accuracy in 5% of the patients in group 1 and in 18% of patients in group 3.