In a companion article in this issue and a previous article in this journal, two experimental enamel dentin adhesive systems were evaluated and compared with four commercially available resin bonding agents by SEM investigation of the tooth adhesive interfaces and by determination of bond strengths to enamel and dentin under various conditions. In continuation of these screening investigations, the present article describes the results of cavity tests for assessment of marginal adaptation by measurement of gap dimensions, and of cavity sealing by rating of microleakage, when standardized dentin cavities were treated with the adhesive restorative systems. Both tests resulted in the same ranking of the six materials. Gluma, Clearfil Photo Bond, and two experimental compounds showed very narrow gaps and moderate microleakage. In contrast, Prisma Universal Bond 2 (the material has been replaced in the market by Prisma Universal Bond 3) and Scotchbond 2 showed significantly wider marginal gaps and more pronounced microleakage. Final discrimination between the efficacy of adhesive restorative materials by any of the currently used in vitro tests is disputable and prediction of long-term clinical performance by laboratory test data remains questionable.