Sporocidal activity of paraformaldehyde tablets was assessed by means of the Association of Official Analytical Chemists technic which is required in Brazil to register this class of sanitizing substances by'the Health Ministery. According to this methodology paraformaldehyde showed sterilizing activity at the 3% (3,0 g/cm³) concentration in 4 hour exposure period at 50ºC in the presence of relative humidity.