The boundary value problem of determining the parameter of an elliptic equation -u''(t)+Au(t)=f(t)+p (0⩽t⩽T), u(0)=φ, u(T)=ψ, u(λ)=ξ, 0<λT, with a positive operator A in an arbitrary Banach space E is studied. The exact estimates are obtained for the solution of this problem in Hölder norms. Coercive stability estimates for the solution of boundary value problems for multi-dimensional elliptic equations are established.