An HPLC method is described using octadecylsilica (3 µm) with an acetonitrile phosphate buffer mobile phase containing diethylamine which is capable of separating ketoconazole [(±)-cis-1-acetyl-4-(4{[2-(dichlorophenyl)-2- (1H-imidazol-1-ylmethyl)-1,3-dioxolan-4-yl]methoxy}phenyl)piperazine] from four related compounds, (R049223, R063600, R053165 and R039519) and from excipients in tablets, cream and shampoo. The method was validated using an external calibration method for tablets, shampoo and creams and a standard addition method for cream. The limits of detection for the related compounds in the presence of ketoconazole are also reported.