Abstract. Let C be a smooth projective curve defined over the finite field Fq (q is odd) and let K = Fq(C) be its function field. Any finite set S of closed points of C gives rise to an integral domain OS := Fq[C − S] in K. We show that given an OS-regular quadratic space (V, q) of rank n ≥ 3, the set of genera in the proper classification of quadratic OS-spaces isomorphic to (V, q) in the flat orétale topology, is in 1 : 1 correspondence with 2Br(OS ), thus there are 2 |S|−1 such. If (V, q) is isotropic, then Pic (OS)/2 classifies the forms in the genus of (V, q). For n ≥ 5 this is true for all genera, hence the full classification is via the abelian group H 2 et (OS, µ 2 ).