The possible excretion of acetylsalicylic acid and salicylic acid into human whole-mouth saliva was studied after the ingestion of 1.0 g of acetylsalicylic acid in gelatine capsules. In addition, the oral clearance of both salicylates was determined after a sham intake of acetylsalicylic acid in solution. No acetylsalicylic acid was excreted in saliva. The maximum concentration of 1.2 mug/ml of the metabolite, salicylic acid, was excreted after 3 hours. Considerable concentrations of both salicylates were retained from 2 to 3 hours in the mouth after the sham intake of the drug in solution. During the retention period, part of the acetylsalicylic acid was hydrolyzed to salicylic acid. In vitro, at low concentration levels about 50% of salicylic acid was bound to salivary proteins. The degree of binding was dependent on the drug concentration. The reason for the absence of excreted acetylsalicylic acid from the saliva was evidently its hydrolysis in the body. Protein binding in the oral cavity may explain the slow clearance of locally applied salicylates. Retention of salicylates in the mouth after the use of drug solutions or effervescent preparations should be considered in, e.g. evaluations of local analgesic effects or bleeding disorders.