We discuss block matrices of the form A = [A(ij)], where A(ij) is a k x k symmetric matrix, A(ii) is positive definite and A(ij) is negative semidefinite. These matrices are natural block-generalizations of Z-matrices and M-matrices. Matrices of this type arise in the numerical solution of Euler equations in fluid flow computations. We discuss properties of these matrices, in particular we prove convergence of block iterative methods for linear systems with such system matrices.