A method for analyzing the matrix composition of Zircaloy-4 (Zr-4) nuclear fuel cladding tubes has been developed, using atom probe analysis. This technique has a spatial resolution of about 1 nm, and makes it possible to measure matrix concentrations, between precipitates, with an accuracy of 0.01% for all elements. Two differently heat treated Zr-4 materials have been analyzed. It was found that the matrix in both materials was highly depleted with respect to iron and chromium. A difference in matrix iron content between the two materials was measured; the material with the longest intermediate annealings at higher temperatures was the least depleted of iron. This difference is explained in terms of iron diffusion to the precipitates during final annealing. The material with high iron concentration in the matrix also showed the best uniform corrosion properties, as tested in autoclave.