beta-N-acetyl-D-glucosaminidase (NAGase) and lysozyme activity were studied in isolated parotid and submandibular saliva collected from five healthy individuals over a 3-wk period. During the first week, saliva samples were collected three times within one specified day (9 a.m., noon, 4 p.m.). Then for each of the following 2 wk, saliva was collected at 9 a.m. of the same day. NAGase activity was determined spectrophotometrically by using p-nitrophenyl-glycoside as substrate. Lysozyme activity was determined turbidimetrically by using Micrococcus lysodeikticus cells as substrate. NAGase and lysozyme were present in all samples of parotid and submandibular saliva. NAGase activity was generally higher in saliva samples collected in the morning and decreased during the day. There was considerable variation in NAGase activity and almost no variation in lysozyme activity in samples taken from the same person. NAGase activity was higher in parotid than in submandibular saliva while lysozyme activity was somewhat higher in submandibular saliva.