This study compared the efficiency of interleukin-6 (IL-6), human neutrophil lipocalin (HNL), C-reactive protein (CRP) and white blood cell (WBC) count for the early detection of postoperative bacterial infections after open-heart surgery. These laboratory markers were determined preoperatively and monitored daily during the first 6 postoperative days. Postoperative bacterial infections were diagnosed in 17 of 54 studied patients needing at least 3 d of intensive care. Patients with less than 3 d of intensive care were not studied. HNL and WBC count showed no significant differences between infected and non-infected groups, whereas both IL-6 and CRP were significantly higher in the infected group. IL-6 levels were higher (p < 0.01) in the infected patients on the first postsurgical day, although with considerable interindividual variation. CRP levels rose on the second postsurgical day and showed less variation (p < 0.01). Calculation of the differences between preoperative and postoperative levels of IL-6 and CRP was not helpful for early detection of postoperative infections. Although IL-6 showed an earlier mean rise than CRP in patients developing postoperative infection, its substantial interindividual variation limits its clinical usefulness. HNL and WBC counts were ineffectual as indicators of postoperative infections in this study.