Septicaemia is a frequent complication in patients with haematological malignancies. In this study we analysed markers of inflammation/immune activation (C- reactive protein, interleukin-6, neopterin), tryptophan metabolites and mannose binding lectin (MBL) levels consecutively in 36 septic patients with haematological malignancies (HM) and non-haematological diseases [intensive care unit (ICU) patients]. During septicaemia different chronological sequences for inflammation markers CRP, IL-6 and neopterin were seen in HM and ICU patients. Septic ICU-patients presented with significantly increased tryptophan degradation and higher neopterin and CRP levels at baseline, while MBL levels were lower in this group compared to subjects with HM. Concentrations of inflammation markers were linked to each other and associated with enhanced tryptophan degradation. Patients who died during follow-up of 28 days tended to have lower baseline MBL concentrations than survivors. Septic patients with HM showed an impaired pro-inflammatory immune response compared to patients with non-haematological diseases.