  We report on our investigations concerning algebraic and transcendental
Brauer-Manin obstructions to integral points on complements of a hyperplane
section in degree four del Pezzo surfaces. We discuss moreover two concepts of
an obstruction at an archimedean place. Concrete examples are given of pairs of
non-homogeneous quadratic polynomials in four variables representing (0,0) over
Q and over Z_p for all primes p, but not over Z. By blow-up, these yield cubic
polynomials in three variables all integral solutions of which satisfy a gcd
condition.
