[en] A laboratory serving a national or international safeguards programme receives product samples or scrap materials of uranium or plutonium of a broad spectrum of matrices for analysis. These materials may have been treated over a wide temperature range rendering them, to varying degrees, refractory. The requirement, therefore, is to be able to measure accurately the uranium or plutonium content in these widely varying material types. The New Brunswick Laboratory (NBL) whose mission is to provide analytical chemistry support for the USA Safeguards programme, has enjoyed considerable success in preparing and analysing a broad spectrum of material types. Results of comparisons of chemical measurements on similar materials prepared by various treatments are discussed. The Safeguards Laboratory either needs a measurement method which is insensitive to other elements or needs to use a simple, selective separation of the desired element. The method of Davies and Gray is highly specific for uranium. Modifications to this method developed by NBL permit unbiased measurements with a routine precision of better than 0.1% (RSD) on samples containing at least 50 mg uranium. The effect of impurity elements on the accuracy and precision of this method has been extensively investigated. A tributyl phosphate (TBP) extraction is compatible with the BNL titrimetric measurement for uranium and provides acceptable removal of all elemental interferents except gold, iodine and technetium. Safeguards analysis of plutonium-containing materials encompasses similar diversity of sample matrices. Investigation of the mechanization of the separation and measurement of plutonium is described. (author)