Rat monoclonal antibodies (MoAbs) against mouse mannan‐binding lectin (MBL)‐A and MBL‐C were generated and assays for MBL‐A and MBL‐C were constructed. This allowed for the quantitative analysis of both proteins for the first time. Previously only MBL‐A has been quantified using less standardized methods. In a mouse serum pool the concentrations were now determined at 7.5 µg MBL‐A and 45 µg MBL‐C per ml. On gel permeation chromatography of mouse serum, MBL‐A eluted corresponding to a Mr of 850 kDa whereas the majority of MBL‐C eluted corresponding to a Mr of 950 kDa. On sucrose density gradient centrifugation the sedimentation velocities of MBL‐A and MBL‐C were estimated at 7.3 S and 10.8 S, respectively. The MBL‐A and MBL‐C levels in 10 laboratory mice strains were compared and found to vary between 4 µg/ml to 12 µg/ml, and 16 µg/ml to 118 µg/ml, respectively. After the induction of acute phase responses by intraperitoneal injection of either casein or lipopolysaccharide (LPS), MBL‐A was found to increase approximately two‐fold, with a maximum after 32 h, while MBL‐C did not increase significantly. In comparison, serum amyloid A component (SAA) peaked at 15 h with an approximate 100‐fold increase.