Most acid-etchant gels are thickened with silica, which can leave a particulate residue on dentinal surfaces. Some newer etchants are thickened with polymers, which reportedly leave no surface residue. This study used scanning electron microscopy to examine dentinal and enamel surfaces that had been etched with either silica- or polymer-thickened gels. The silica gels left particulate debris on dentinal surfaces, and this debris was not removed by rinsing with water. There was little evidence of this contaminant on enamel surfaces. Enamel and dentinal surfaces treated with the polymer-thickened gels appeared to be clean and uncontaminated. Shear bond strengths of composite resin to enamel and dentin etched with the different types of gel etchants were also evaluated. Silica contamination did not adversely affect bonding. in fact, etching with silica-thickned gels resulted in slightly higher bond strengths to both substrates. However, the differences were not statistically significant.