A novel assay method has been developed and validated, using surface plasmon resonance (SPR), for quantitation of cetuximab (C225) in monkey serum. By injecting non-labeled antibody samples onto a biosensor surface on which epidermal growth factor receptor (EGFR) was immobilized, the concentration of C225 can be accurately measured. This assay has a range of reliable response from 0.05 to 50 microg/ml C225 in monkey serum, which was well fitted with a sigmoidal model. The immobilized EGFR was found to be stable for at least 100 regeneration cycles at room temperature. Intra- and inter-assay CVs ranged from 3.20% to 8.89% and from 5.93% to 11.11%, accuracy from 92% to 107.52% and from 90% to 106.88%, respectively. Matrices such as 50% human serum, 50% Sprague Dawley rat serum, chimeric recombinant anti-CD20 monoclonal antibody, human gamma-globulin and chimeric recombinant her2 antibody did not interfere with C225 analysis on the sensor surface. This is the first report on the quantitation of C225 in monkey serum by an optical biosensor technology. This method was used to characterize the pharmacokinetics of C225 in rhesus monkeys. After a single-dose of intravenous infusion administration of 7.5, 24 and 75 microg/kg, average C(max) ranged from 168+/-28 to 1624+/-113 microg/ml, and AUC(0-infinity) ranged from 15,739+/-1059 to 295,017+/-44,533 microg h/ml. C225 elimination followed a bi-exponential profile with t(1/2) ranging from 2.7+/-0.7 to 6.7+/-0.1 h. It was non-linear serum pharmacokinetics of C225 across the investigated dosage range in monkeys (7.5-75 mg/kg).