Rapid diagnosis of bloodstream infections (BSIs) in the emergency department (ED) is challenging, with turnaround times exceeding the timeline for rapid diagnosis. We studied the usefulness of procalcitonin as a marker of BSI in 367 adults admitted to our ED with symptoms of systemic infection. Serum samples obtained at the same time as blood cultures were available from 295 patients. Procalcitonin levels were compared with blood culture results and other clinical data obtained during the ED visit. Procalcitonin levels of less than 0.1 ng/mL were considered negative; all other levels were considered positive. In 16 patients, there was evidence of BSI by blood culture, and 12 (75%) of 16 patients had a procalcitonin level of more than 0.1 ng/mL. In 186 (63.1%) of 295 samples, procalcitonin values were less than 0.1 ng/mL, and all were culture negative. With a calculated threshold of 0.1475 ng/mL for procalcitonin, sensitivity and specificity for the procalcitonin assay were 75% and 79%, respectively. The positive predictive value was 17% and the negative predictive value 98% compared with blood cultures. Procalcitonin is a useful marker to rule out sepsis and systemic inflammation in the ED.