“…A special problem is the preparation of milk urea standards for adequate calibration of different methods. This has been submitted to experiments and methodical examination, including the mutual result relationships of the methods, which are interpreted as potentially reference and other direct or indirect ones (for example filter MIR technology), frameworkly in the following fields: -the preparation of calibration standards for different methods of MUC determination, potentially for urea determination in other body fluids (Wolfschoon-Pombo et al, 1981;Oltner et al, 1985;Hanuš et al, 1995Hanuš et al, , 1997; -the examination, development, construction and validation of enzymatic sensors, reactors, and potentially biosensors for the analysis of urea concentration in different biological materials, especially in milk (Guilbault and Montalvo, 1970;Sundaram, 1979;Thavarungkul et al, 1991;Sansubrino and Mascini, 1994;Koncki et al, 1995;Ciana and Caputo, 1996;Sheppard et al, 1996); -the validation of the relationships of recently developed principles and methods of MUC determination or urea determination in blood to the current methods or to potentially reference ones, mostly specific ureolytical ones (Broutin, 2000); -a notice of problems of recovery and reliability of urea determination under the conditions of mid filter transmission infrared technology (MIR) in comparison with validated methods, where the determination coefficient of accuracy was about 50% (Here, 1998). The aim of this study was to evaluate the relationships between the currently used principles of methods of MUC determination in the Czech Republic, especially of new modern methods (measurement in the main area of infrared spectrum with use of Fourier transformations, FT-MIR; Lefier et al, 1996), on artificially constructed control samples on the milk basis and to deduce the relevant methodical recommendations for enhancement of reliability and improvement of practical interpretation of produced analytical results due to obtained theoretical relationships.…”