Aims: Adherence of Mycoplasma hyopneumoniae to the ciliated epithelial cells of the porcine respiratory tract is considered an important first step in the pathogenesis of enzootic pneumonia. It was the aim of this study to verify the usefulness of in vitro adhesion as a virulence marker. Methods and Results: Adherence capacity to immobilized cilia from porcine tracheal epithelial cells of three low, two moderately and two highly virulent M. hyopneumoniae field isolates was determined by a microtitre plate adherence assay. Conclusions: No significant differences between the isolates were demonstrated. Significance and Impact of the Study: The results suggest that mechanisms other than adherence might be responsible for the observed differences in virulence of these field isolates or that the in vitro assay does not adequately reproduce in vivo adherence conditions.