Lactoperoxidase (LPO)/H2O2/SCN(-)-system-generated hypothiocyanite ions (OSCN-) and hypothiocyanous acid (HOSCN) are inhibitory against a number of oral bacteria, including mutans streptococci. A commercially available toothpaste (Biotene) comprises the complete LPO system. Generation of HOSCN/OSCN- by Biotene was studied in vitro both in sterilized and nonsterilized saliva of 10 healthy subjects. The HOSCN/OSCN- yield ranged from 100 to 300 microM with Biotene, while the salivary levels of HOSCN/OSCN- before the addition of Biotene were 30.1 +/- 25.1 microM. Two in vivo trials were carried out. In the first study, resting saliva was collected from 12 individuals before, immediately after, and 2, 5, 10 and 20 min after brushing with Biotene to evaluate the in vivo generation and decomposition of HOSCN/OSCN-. In the second study, 26 healthy individuals attended a 1-month crossover trial with Biotene and a control toothpaste, Vademecum (no LPO system), both containing F- and xylitol. The salivary counts of total streptococci, mutans streptococci (MS), lactobacilli and the total flora (TF), as well as the peroxidase, thiocyanate ion and HOSCN/OSCN- levels were determined before and after 2 and 4 weeks daily use of the toothpastes. Twice-a-day use of Biotene for 1 month resulted in an elevation of 'resting levels' of HOSCN/OSCN-. No such effect was found with the control toothpaste. No significant changes were found in the salivary levels of total streptococci, MS, lactobacilli or TF after 1-month use of either toothpaste. The results show the capability of the LPO-system-containing toothpaste to elevate the salivary levels of HOSCN/OSCN-, although no bactericidal effect was observed.