Abstract. We revisit with another view point the construction by R. Brylinski and B. Kostant of minimal representations of simple Lie groups. We start from a pair (V, Q), where V is a complex vector space and Q a homogeneous polynomial of degree 4 on V . The manifold Ξ is an orbit of a covering of Conf(V, Q), the conformal group of the pair (V, Q), in a finite dimensional representation space. By a generalized Kantor-Koecher-Tits construction we obtain a complex simple Lie algebra g, and furthermore a real form g R . The connected and simply connected Lie group G R with Lie(G R ) = g R acts unitarily on a Hilbert space of holomorphic functions defined on the manifold Ξ.