The aim of our study is to analyse the contamination level of air, water and hard surfaces before and after works activities in a dental clinic. Four different methods are detected for the sampling of the hard surfaces: contact plates, nitrocellulose membranes, swab and mask system, bioluminometer. Our results are overall satisfactory, but few critical situations related to some practice, were observed. In comparing the four methods of sampling the hard surfaces, the use of bioluminometer although referring to indirect indices, appears to give results comparable to those obtained with the contact plates and nitrocellulose membranes, which determine the microbiologic count. Contact plates and nitrocellulose membranes appear to be of more friendly use and show same results.