OBJECTIVE: Ficolin-3 is a serum protein of putative importance in autoimmunity. Our objective was to investigate any differential expression of ficolin-3 in patients with systemic lupus erythematosus (SLE) or its clinical subsets. METHODS: Serum levels of ficolin-3 (S-ficolin-3) were determined in 95 patients with SLE and 103 healthy controls using an ELISA. RESULTS: Median S-ficolin-3 was 56.1 microg/ml (range 0 to >or=87.3) and 32.4 microg/ml (10 to >or=87.3) in patients and controls, respectively (p<0.001). Increased S-ficolin-3 was associated with hemolysis, positive Coombs test, and lymphopenia, but not with SLE Disease Activity Index scores or C-reactive protein. In one patient without detectable S-ficolin-3, the FCN3 gene appeared normal. CONCLUSION: The elevation of S-ficolin-3 and its association with specific manifestations in SLE may indicate a pathogenetic role of ficolin-3 in SLE.