High serum concentrations of procalcitonin (PCT), the 116 amino acid precursor protein of the hormone calcitonin, have been found in patients with various bacterial infections, particularly in those with sepsis. Because recent reports have shown that serum PCT constitutes a useful parameter for the diagnosis of sepsis in patients with several clinical conditions, a temporal analysis of the PCT concentrations in the plasma of 19 patients with severe burns (median body surface area burned, 32%) was conducted retrospectively. Nine patients were classified as septic on the basis of standardized clinical and laboratory parameters. Compared with the nonseptic group, these patients showed higher plasma PCT throughout the study period (median concentrations of septic vs nonseptic patient groups: 0.4 vs 0.2 μg/L on postburn day 2; 1.0 vs 0.3 μg/L on postburn day 4; 5.5 vs 0.3 μg/L on postburn day 7; 10.8 vs 0.5 μg/L on postburn day 9; 4.2 vs 0.4 μg/L on postburn day 12; and 1.7 vs 0.5 μg/L on postburn day 14), with differences considered to be significant (P< .05) from day 7 on. In contrast, differences in the plasma C-reactive protein concentrations were less pronounced and never reached statistical significance. PCT concentrations exceeding 15 μg/L were only observed in the 3 patients who died of sepsis-induced multiple organ failure. In addition to absolute PCT, individual time courses were also of diagnostic value. PCT is a highly efficient laboratory parameter for the diagnosis of severe infectious complications after a burn injury. (J Burn Care Rehabil 1999;20:354–60)