[en] A method is described for the determination of La, Ce, Pr and Nd in carbon steels by optical emission spectroscopy (OES). The method involves preconcentration of the four rare earth metals as fluorides in the presence of yttrium as carrier. During preconcentration, the maxtix Fe, is removed as soluble fluoride. The preconcentrated sample consisting of yttrium and microgramme quantities of the four rare earth metals, is ground with conducting graphite powder in the ratio 1:1 by weight. Standards have La, Ce and Nd in the concentration range 20-500 ppm and Pr in the range 50-500 ppm, are prepared using wet procedure. The spectra of samples and standards are recorded on a Jarrell-Ash 3.4 m Ebert plane grating spectrograph, with 30,000 l.p.i. grating in the wavelength region, 4200-4500 A, second order. Eight milligrammes each of sample and standard loaded in the cavity of a 1/4 U.C.C. graphite electrode are arced at 8 amp d.c. with an exposure time of 30 seconds. The relative standard deviation (RSD) ranges from +-7.4(La) to +-17.9per cent (Pr). (author)