There are some colorimetric procedures for determining available phosphorous in soils, and phosphorous is evaluated by means of a blue complex (phosphomolibdic acid); in one of the methods, color appear when ascorbic acid is used as reductor agent, and in the other when stannous chloride is used. Both methods use the same extractive solution Bray II due to its good response for acid soil cultures, like most Colombian soils are. When the two methodologies were compared it was found that the most sensible method and with the best limit of detection and quantification was the one that uses ascorbic acid, antimonioum and potassium tartrate. Its variation coefficients and standard de81 REVISTA COLOMBIANA DE QUIMICA, VOLUMEN 35, No. 1 DE 2006 * Departamento de Quimica, Facultad de Ciencias, Universidad Nacional de Colombia, Bogota. ** Departamento de Quimica, Facultad de Ciencias, Universidad Nacional de Colombia, Bogota. Correo electronico: miballesterosg@unal.edu.co viation were lower, and for this reason it is considered as the most precise method for phosphorous determination.