Abstract. Using abstract interpolation theory, we study eigenvalue distribution problems for operators on complex symmetric Banach sequence spaces. More precisely, extending two well-known results due to König on the asymptotic eigenvalue distribution of operators on p-spaces, we prove an eigenvalue estimate for Riesz operators on p-spaces with 1 < p < 2, which take values in a p-concave symmetric Banach sequence space E → p, as well as a dual version, and show that each operator T on a 2-convex symmetric Banach sequence space F , which takes values in a 2-concave symmetric Banach sequence space E, is a Riesz operator with a sequence of eigenvalues that forms a multiplier from F into E. Examples are presented which among others show that the concavity and convexity assumptions are essential.