Extrinsic staining of teeth is a side-effect of some antiseptic mouthrinses. However, few of the many rinse products available to the general public have been investigated for their propensity to cause staining. Dietary factors play an aetiological role in staining and have been used in vitro to study and compare the activity of rinses. The aim of this study was to assess rinse products for staining in vitro and, through the staining reaction, to compare the activity of products containing the same ingredients. Perspex blocks, with or without saliva pretreatment, were soaked in rinses for 2 min, washed and placed in a standard tea solution for 60 min and then the optical density (OD) read on a spectrophotometer. The cycle was repeated 10 times for saliva and 17 times for no saliva specimens or until the maximum OD was exceeded. A series of three separate experiments was performed by this method. The maximum OD was not exceeded by any product before seven passages and therefore data were compared at six passages. For most products OD increased with saliva pretreatment. Some cetylpyridinium chloride (CPC) rinses stained comparably to a chlorhexidine rinse. CPC rinses, most of which contained the same concentration of the antiseptic, varied considerably in their propensity to induce staining and one was little different to water controls. A 0.1% chlorhexidine rinse stained slightly more than a 0.2%. A phenolic/essential oil product produced some staining but zinc, triclosan and other essential oil rinses did not stain.(ABSTRACT TRUNCATED AT 250 WORDS)