The influence of dentinal fluid and of a number of stress procedures on the quality of the margins of class V restorations located in both enamel and dentin was quantitatively assessed in vitro with the aid of a scanning electron microscope. The materials tested were GLUMA 2000 experimental, Prisma Universal Bond 3, and Syntac, together with the fine hybrid composites supplied by the respective manufacturers (Pekafill, AP.H, and Tetric). All materials achieved over 95% of "continuous margin" in enamel before and after stressing. In dentin, the initial values, with as well as without dentinal fluid simulation, were situated between 93.2 and 98.2%. With GLUMA 2000 experimental after stressing, a "continuous margin" occurred in only 50.2%, but with Prisma Universal Bond 3 and Syntac, the value was 79.0%. The influence of dentinal fluid simulation was dependent on the dentinal adhesive used. The effects of the various stress procedures were not significantly different.