Background. Fluorescence imaging hardware (SPY) has recently been developed for intraoperative assessment of blood flow via detection of probes emitting in the nearinfrared (NIR) spectrum. This study sought to determine if this imaging system was capable of detecting micrometastatic head and neck squamous cell carcinoma (HNSCC) in preclinical models. Methods. A NIR fluorescent probe (IRDye800CW) was covalently linked to a monoclonal antibody targeting epidermal growth factor receptor (EGFR; panitumumab) or nonspecific IgG. HNSCC flank (SCC-1) and orthotopic (FADU and OSC19) xenografts were imaged 48-96 h after systemic injection of labeled panitumumab or IgG. The primary tumor and regional lymph nodes were dissected using fluorescence guidance with the SPY system and grossly assessed with a charge-coupled NIR system (Pearl). Histologic slides were also imaged with a NIR chargedcoupled device (Odyssey) and fluorescence intensity was correlated with pathologic confirmation of disease. Results. Orthotopic tongue tumors were clearly delineated from normal tissue with tumor-to-background ratios of 2.9 (Pearl) and 2.3 (SPY). Disease detection was significantly improved with panitumumab-IRDye compared to IgG-IRDye800 (P<0.05). Tissue biopsy samples (average size 3.7 mm) positive for fluorescence were confirmed for pathologic disease by histology and immunohistochemistry (n = 25 of 25). Biopsy samples of nonfluorescent tissue were proven to be negative for malignancy (n = 28 of 28). The SPY was able to detect regional lymph node metastasis (<1.0 mm) and microscopic areas of disease. Standard histological assessment in both frozen and paraffinembedded histologic specimens was augmented using the Odyssey. Conclusions. Panitumumab-IRDye800 may have clinical utility in detection and removal of microscopic HNSCC using existing intraoperative optical imaging hardware and may augment analysis of frozen and permanent pathology. © Society of Surgical Oncology 2012.