The present paper has the objective of verifying the variability of the values of the main biométrie relations used in the identification of Micropogon furnieri (Desmarest, 1822) Jordan, 1884 and also of verifying the possibilities that this relations could be used in the separation of the independent populations that live in the Uruguayan district of the Argentinian zoogeographic province and in the transition zone between this last one and the south Brazilian zoogeographic province. Three fishing areas were examined: area I - in between the latitudes of 29º30'S and 31º30'S, related to the mouth of the Tramandai River; area II - in between the latitudes of 31º30'S and 33º00'S, related to the mouth of the Grande River; area III - in between the latitudes of 35º00'S and 36º30'S, related to the mouth of the La Plata River. The conclusions resulting from the study are: 1 - The relations between the total length and any of the other elements (total weight, standard length, maximum height, head length, snout length, eye diameter and intestine length), with reference to the sex and fishing areas and inside the limits of total length variation from 34 to 60 cm, extremes included, do not allow the acceptance of the existence of independent populations in the different fishing areas; 2 - The relation total length/total weight, independent of the sex and fishing areas and inside the limits of total length variation from 34 to 60 cm, extremes included, shows and almost uniform increase of the total weight from 410 to 2,310 g; 3 - Independent of the sex and fishing areas, and inside the limits of the total length variation from 34 to 60 cm, extremes included, can be observed the following amplitudes of variation expressed as percentage of total length and corresponding to each other biometric clement, as standard lenght - from 83 to 87%, maximum height - from 22 to 28%, head length - from 24 to 28%, snout length - from 8 to 11%, eye diameter - from 3 to 5%, intestine length - from 110 to 225%.
