Liquid chromatography-mass spectrometry (LC-MS) affords a highly promising solution for absolute quantification of biotherapeutics/targets in tissues, which is critical for drug development. Nonetheless, accurate/robust tissue quantification remains challenging largely owing to the lack of optimal approaches to address the following fundamental prerequisites: (i) efficient removal of residual blood without losing tissue-associated biotherapeutics; (ii) an optimal method to exhaustively/quantitatively recover target proteins from tissues; and (iii) an appropriate strategy to prepare calibration/quality-control samples to ensure accurate tissue analysis. Here, we devised novel analytical procedures enabling extensive and systematic investigation of the above issues and thereby development of optimal strategies for accurate tissue analysis. Key discoveries include: first, using a novel procedure of sequential administration of nonlabeled and then stable-isotope-labeled monoclonal antibody (mAb); it was determined that perfusion with three blood volumes of heparinized saline is optimal, achieving efficient blood removal (95-99%) and low quantitative bias (0.5-13%); second, a reference sample set established by mass-balanced, exhaustive extraction, permitted accurate measurement of absolute protein recovery from tissues of dosed animals; with this method, we found mAb biotherapeutics present in free-(49.3-75.4%) and bound-forms (24.6-50.7%) in tissues, even without a target; therefore, a denaturing detergent buffer is necessary for exhaustive extraction (recovery>90%); third, overnight-incubation of calibration samples after spiking mAb to tissue was found to improve quantitative accuracy, especially for nondenaturing buffer extraction. These investigations established the critical parameters and optimal protocols that can be universally applied to achieve accurate and robust quantification of biotherapeutics/targets in tissues. As a proof of concept, we conducted the first-ever extensive pharmacokinetics measurement of mAb in major tissues with a LC-MS-based method, where interesting features of mAb tissue disposition were observed.