The 4-year results of a fissure sealant trial are reported. Glass polyalkenoate and bis GMA sealant were applied to 590 first permanent molar teeth using a half mouth study design in a group of 228 6-8-year-old children. Similar cariostasis was observed for the two materials at the end of 4 years despite marked differences in retention. Polyalkenoate cements probably should be regarded as 'fluoride depot' materials rather than fissure sealants when used in this context.