Tesis de doctorado en ciencias matemáticasThe aim of this dissertation is to present an example about the A00 property of el­ lipt ic measure (with respect to surface measure) associated to second order divergence form operators with bounded measurable coefficients, when the discrepancy between the main coefficients of the operators is supported on Whitney type rectangles of the unit ball of IRn. In particular the discrepancy between the coefficients does not satisfy a Carleson measure condition, nor the coefficients of the operators involved are radi­ ally independent, as in former well known papers [8, 17, 18, 2]. As an application of the perturbation results, we provide a class of operators with coefficients supported on Whitney type rectangles, for which the A00 property holds.Universidad deSonora, División de Ciencias Exactas y Naturales, Programa de Posgrado en Matemáticas 2014