The document compares the use of LC-MS/MS versus ELISA for the bioanalysis of three monoclonal antibodies (adalimumab, rituximab, and trastuzumab) in rat and mouse pharmacokinetic studies. The LC-MS/MS method showed higher sensitivity, dynamic range, and selectivity compared to ELISA, though it had lower throughput and higher costs. Results from the two methods showed good concordance for adalimumab and trastuzumab in rats, demonstrating LC-MS/MS as a viable alternative to ELISA for bioanalysis of large molecules.