Two series of experiments were performed in order to compare the ability of different cationic antiseptics to inhibit the acid production in plaque. In addition an attempt was made to evaluate the influence of oral retention on the acid-inhibiting properties of these agents. In one series of experiments acid production, following sucrose applications on plaque, was measured in situ prior to and at given time intervals after rinsing with the individual agents. In a second series the effect of eluting the antiseptics retained in the oral cavity by means of 5 consecutive acetic acid (6 mM) rinses was evaluated. The results showed that chlorhexidine (0.5 mM) was more effective than benzalkonium chloride (1 mM) and piperazine (1 mM). Cetylpyridinium chloride (1 mM) was the least effective. Acidic elution markedly reduced the inhibitory effect of single rinses of chlorhexidine (0.5 mM), benzalkonium chloride (1 mM) and the cetylpyridinium chloride (1 mM). This effect was less pronounced with a higher concentration (2.2 mM) of chlorhexidine. The results gave support to the view that retention of an agent in the mouth and in plaque is of significance for its ability to inhibit acid production of dental plaque.