A second-derivative UV spectrophotometric method for the simultaneous determination of medazepam and hyoscine butylbromide in sugar-coated tablets without prior separation is described. In the derivative spectrophotometric determination of these drugs, calibration graphs were obtained by plotting peak-trough amplitudes at 252.6 and 264.8 nm versus concentration of medazepam and zero-crossing amplitude at 212.5 nm versus concentration of hyoscine butylbromide. The relative standard deviation of the method was found to be +/-0.56% for medazepam and +/-0.08% for hyoscine butylbromide. This method has been successfully applied to tablets containing medazepam and hyoscine butylbromide. (C) 1998 Elsevier Science S.A.