We study multiple 3-branes on an F theory orientifold. The world-volum
e theory of the 3-branes is d = 4, N = 2 Sp(2k) gauge theory with an a
ntisymmetric tensor and four flavors of matter in the fundamental. The
solution of this gauge theory is found for vanishing bare mass of the
antisymmetric tensor matter, and massive fundamental matter. The inte
grable system underlying this theory is constructed.