The paper is concerned with
establishing the existence of eigenvalues for the second order differential
system y′ = k(x,λ)z, z′ = g(x,λ)y, together with boundary conditions
y(a) = A(λ)y(b) + B(λ)z(b), z(a) = C(λ)y(b) + D(λ)z(b). A general theorem
is obtained establishing the existence of eigenvalues for both self-adjoint
and nonself-adjoint boundary problems. This result is then simplified for
nonself-adjoint problems, extending the previous work of H. J. Ettlinger and E.
Kamke.