Objectives/Hypothesis: To determine whether measurement of pepsin in throat sputum by immunoassay could be used as a sensitive and reliable method for detecting laryngopharyngeal reflux (LPR) compared with 24-hour double-probe (esophageal and pharyngeal) pH monitoring. Study Design: Patients with clinical LPR undergoing pH monitoring provided throat sputum samples during the reflux-testing period for pepsin measurement using enzyme-linked unmunoadsorbent assay. Results: Pepsin assay results from 63 throat sputum samples obtained from 23 study subjects were compared with their pH monitoring data. Twenty-two percent (14/63) of the sputum samples correlated the presence of pepsin with LPR (pH ≤ 4 at the pharyngeal probe), of which the median concentration of pepsin was 0.18 μg/mL (range 0.003-22 μg/mL). Seventy-eight percent (49/63) of the samples unassociated with (pharyngeal) reflux contained no detectible pepsin. Mean pH values for pepsin-positive samples were significantly lower than negative samples at both esophageal probe (pH 2.2 vs. pH 5.0) (P < .01) and the pharyngeal probe (pH 4.4 vs. pH 5.8) (P < .01). When the pepsin assay results were compared with the pharyngeal pH data for detecting reflux (events pH ≤ 4), the pepsin immunoassay was 100% sensitive and 89% specific for LPR. Conclusions: Detection of peps in in throat sputum by immunoassay appears to provide a sensitive, noninvasive method to detect LPR. © 2005 The American Laryngological, Rhinological and Otological Society Inc.