We queried DNA from saliva or plasma of 93 HNSCC patients, searching for somatic mutations or human papillomavirus genes, collectively referred to as tumor DNA. When both plasma and saliva were tested, tumor DNA was detected in 96% (95% CI, 84% to 99%) of 47 patients. The fractions of patients with detectable tumor DNA in early- and late-stage disease were 100% (n=10) and 95% (n=37), respectively. Saliva is preferentially enriched for tumor DNA from the oral cavity, whereas plasma is preferentially enriched for tumor DNA from the other sites. Tumor DNA in the saliva and plasma is a valuable biomarker for detection of HNSCC.