Xibornol [6-(isoborn-2-yl)-3,4 xylenol] is a highly lipophilic and poorly soluble drug used as spray mouthwash for the local treatment of infection and inflammation of the throat and in the dental care, due to both its bacteriostatic activity, mainly against Gram positive micro-organisms and its antiviral properties. The drug concentration required for the therapeutic activity is 3% (w/v). Its poor water solubility makes difficult to set up drug formulations based on aqueous solvents, so xibornol is at present commercially available only as spray aqueous suspension. The self-microemulsifying approach was found to be effective to formulate stable and pharmaceutically acceptable liquid spray formulations of xibornol. The minimal inhibitory concentrations (MIC) and the minimal bactericidal concentrations (MBC) of xibornol against 100 strains of Staphylococcus aureus, clinically isolated have been evaluated in range between 2 ug/ml and 8 ug/ml. In the patients treated with xibornol (500 mg every 8 h for 7 days) any modification in phagocytosis frequency (PMF), phagocytosis index (PHI), nitroblue tetrazolium (NBT), reduction frequency (NRF), microbicidal activity and neutrophil mobility of PML, before, during and after the end of therapy wasn’t found.