In two apparently homogeneous areas of Oxisol, soil samples both from the surface (0-30 cm) and from the subsurface (80-120 cm) were collected in each of the areas, following a 50 m grid pattern. Each soil sample was analised in order to be classified and to be verified under the soil survey point of view the distribution of the mapring units as well as their frequency of occurence with diminishing degree of generalization of the taxonomic classes according to the American soil classification system of 1970. The results obtained for both areas led to the following conclusions: a) Morphological characteristics were found to be very homogeneous for surface and subsurface samples. Excluding the petroferric contact and the soil depth in area-2, the morphological characteristics were unsuitable to differentiate classes in both areas. b) The classification of the soils in the great group level based on field observation alone was found to be not suitable as the differentiation of the units Oxisols depends on the analytical characteristics, and it was not possible, in these areas to relate the morphology with the analytical data. c) The categories of family for area-1 and subgroup for area-2 were considered the more adequate for the semi-detailed level of soil survey and the scale of publication of the map of 1:50,000.