Intensive care patients with organ failure often suffer an acute catabolic state. Leptin is a 16-kDa hormone which is produced by mature adipocytes and correlates with human energy expenditure. We investigated whether continuous venovenous haemofiltration, which may eliminate molecules up to 20–30 kDa, is capable of removing human leptin. Leptin measurements were made in the plasma of 15 patients with sepsis before continuous venovenous haemofiltration (T0) and during the procedure at 24 h (T1), 48 h (T2), and 72 h (T3), using samples taken before and after haemofiltration. In addition, measurements were made in the ultrafiltrate at T1–T3. The plasma leptin level at T0 was 17.6 ng mL−1. The concentration at T1 was 17.5 ng mL−1 pre-filter and 26.5 ng mL−1 post-filter (T2: 14.2/23.2 ng mL−1; T3: 12.4/16.3 ng mL−1).This concentration effect after haemofiltration was also seen with albumin. The values measured at T3 tended to be lower than those recorded at T1. The mean leptin levels in the ultrafiltrate were 0.15–0.18 ng mL−1. The range of leptin levels in the ultrafiltrate was thus only 0.5–3% of that measured in plasma. We conclude that human leptin is only minimally elimininated into the ultrafiltrate by continuous venovenous haemofiltration and that plasma leptin levels may decrease during sepsis.