AIMS: To investigate staining patterns for mannan binding protein (MBP) by immunocytochemistry in liver biopsy specimens from patients with various hepatic disorders; to measure the serum MBP concentration in the patients at the time of biopsy; and to compare these to define further the role of MBP in disease. METHODS: Fifty seven consecutive patients with a variety of types of liver disease were studied. Fresh liver biopsy specimens were immunostained with anti-MBP and graded for intensity of staining. Serum MBP concentrations were measured on samples obtained on the day of biopsy, as were a full range of liver blood tests. RESULTS: MBP was only detectable in liver biopsy specimens from patients with morphological evidence of liver disease. MBP was most prominent in the livers of patients with severe alcoholic liver disease; livers harbouring metastases or showing biliary disease had moderate concentrations. Patients with liver disease were more likely to have raised serum MBP concentrations, but there was no correlation between these values and those found in the biopsy specimens. There was also no significant correlation between either of these concentrations and liver blood test abnormalities. CONCLUSIONS: Patients with liver disease tend to have raised MBP concentrations in both the liver and serum, but the exact relation between the two is as yet undefined.