Sections of demineralized teeth which had received experimentally inserted restorations using a variety of materials have been stained according to the Brown and Brenn technique. Conventional cavity preparations had been made in intact areas and the cavities were dried gently without additional treatment prior to restoration. Different restorative materials were used and the teeth were extracted after 3-117 days' observation. No bacteria could be demonstrated at the dentin/filling interface or in the dentin if zinc oxide/eugenol, Ca(OH)2 mixed with water or corticonsteroid/antibiotic preparations were employed as base or lining materials. A few bacteria were found subjacent to two of seven unlined amalgam fillings and subjacent to three silicate restorations which had been lined with a polymeric material.