The in vivo effect of some cations on the amount of lipoteichoic acid (LTA) formed in plaque was investigated in two studies. In the first part five students followed six mouthrinsing programs, each of which lasted 4 d. Rinsing was performed for 1 min every second hour with a test solution (0.05% stannous fluoride (SNF2); 0.05% chlorhexidine gluconate; 0.3% lanthanum chloride (LaCl3) and 0.05% sodium fluoride (NaF), followed 5 min later with a rinse of a 15% sucrose solution. Sucrose alone and xylitol rinses were used as controls. The second part involved a group of 10 students rinsing for 1 week four times daily with a sucrose solution, and for another week four times daily with the same source sucrose solution and in addition, three times daily with a 0.05% SnF2 solution. The individual plaque samples were collected after each rinse program, made into a suspension and then divided for protein analysis, carbohydrate analysis and estimation of LTA by phenol extraction and indirect hemagglutination against a specific antiserum. The total amount of plaque formed and the LTA content were reduced in sucrose plaque by the chlorhexidine and SnF2 rinse programs, or when xylitol replaced sucrose as the main sugar source. There was no significant effect with LaCl3 or NaF. The rinse produced changes in the clinical appearance of the plaque.