  We compute the partition functions of D(-1)D7 systems describing the
multi-instanton dynamics of SO(N) gauge theories in eight dimensions. This is
the simplest instance of the so called exotic instantons. In analogy with the
Seiberg-Witten theory in four space-time dimensions, the prepotential and
correlators in the chiral ring are derived via localization formulas and found
to satisfy relations of the Matone type. Exotic prepotentials of SO(N) gauge
theories with N=2 supersymmetries in four-dimensions are also discussed.
