Abstract.Bloch, and later H. Cartan, showed that if Hx, ... , Hn+2 are n + 2 hyperplanes in general position in complex projective space Pn , then Pn -Hx U ■ ■ • U Hn+2 is (in current terminology) hyperbolic modulo A , where A is the union of the hyperplanes (Hxn---(~)Hk)® (Hk+X n • • ■ n Hn+2) for 2 < k < n and all permutations of the Hi. Their results were purely qualitative. For n = 1 , the thrice-punctured sphere, it is possible to estimate the Kobayashi metric, but no estimates were known for n > 2. Using the method of negative curvature, we give an explicit model for the Kobayashi metric when n = 2 .Pour arriver à des résultats d'ordre quantatif, il faudrait construire... la fonction modulaire.Henri Cartan 1928 0. Introduction For a compact complex manifold M, Brody [5] has given a simple criterion for hyperbolicity: M is hyperbolic if and only if every holomorphic map /: C -► A/ is constant. For noncompact manifolds, hyperbolicity is much more difficult to establish, as Brody's Theorem is false (Green's example, see [14]). The situation is even more complicated for hyperbolicity modulo a subset, the most general case. In this paper we give an explicit model for the Kobayashi metric on a particular X, namely P2 minus 4 lines. We prove that the model does indeed