Background <p>Some non-resorbable membranes are indicated to be left exposed in the oral cavity during regeneration procedures. Given the frequency or indication of exposure of these membranes in the oral cavity, it is worth studying their pattern of contamination, which may lead to undesirable clinical results.</p> Purpose <p>This study aimed to evaluate and compare microbial contamination among non-resorbable membranes intended for exposure in the oral cavity during regenerative procedures.</p> Methods <p>Samples of non-resorbable membranes were used: Bone Heal^® (BH), Cytoplast Txt-200^® (CT), Lumina PTFE^® (L), and Surgitime Titanium Seal^® (STS). Fifty-six samples were divided into groups: group S (control) – sterile membranes; group C – membranes contaminated with human oral biofilm. These samples were analyzed by counting colony-forming units and scanning electron microscopy/energy dispersive spectroscopy. One-way ANOVA and Tukey’s tests were used to compare colony-forming units among the contaminated groups. The paired t-test was used to compare the colony-forming units between the two groups of each membrane, with a significance level of 5%.</p> Results <p>The membranes showed similar contamination values, with the BH membrane being the least contaminated and the L membrane the most contaminated (<i>p</i> = 0.005). The membranes presented surfaces with different patterns and designs, also showing different levels of contamination that seem to be related to surface characteristics and composition.</p> Conclusion <p>All studied membranes intended for exposure in the oral cavity became contaminated, showing different patterns, with membrane BH exhibiting the lowest contamination.</p>