Nowadays we are witnessing an ever growing use of rare earth metals (REM) for industrial purposes. Apart from their classic utilization in the manufacturing of explosives, glass and ceramics, they have now become important in the electronics industry, the production of semiand superconductors, microwave techniques and the fabrication of luminescent materials. In connection with their analysis, their role in nuclear reactor techniques must also be mentioned: some of the REM which have a large cross-section for neutron capture are important reactor poisons. Owing to the similar outer electronic shell structures of the different REM elements, the determination of almost each species requires several physical analytical methods. The classic gravimetric and titrimetric procedures lend themselves generally only to the determination of the total quantity of REM in a sample. 1-3 Small total REM contents can be determined by various spectrophotometric methods. ~ For trace quantities of different REM the determination can be performed by the generally used trace analytical methods, such as mass spectrometry, 5 emission spectrometry, X-ray fluorescence analysis, 6'7 emission and absorption flame photometry, s,9 and the various luminescence techniques; 1~ however, as regards both performance and frequency of application, activation analysis plays a preponderant part in REM determination. Table 1, constructed from the data of COSGROVE et al. 7 and MORRISON? 3 shows the potentialities of the different methods, but it should be noted that the numerical values refer mostly to the ideal case (i.e. the absence of any interfering element, under optimum experimental conditions), and essentially they can be used only for the comparison of the different methods. In practice, one has to consider such factors as the nature of the matrix, interference from the simultaneously present REM species, problems of the pretreatment and incidental chemical separations, time consumption, the achievable accuracy, the given conditions and the cost factors arising from all this. TM Although activation analysis may be the most frequent choice for the solution of analytical problems, as it is in the case of REM, this method is still far from being considered an industrial technique. Nevertheless, to quote LYON,