Abstract.The twistor lifts of a minimal surface in a constantly curved 4-space are studied. Computing the Laplacian of the length of their differentials provides a topological condition for pseudoholomorphicity. Geometric conditions for holomorphicity of surfaces in flat spaces are found.The pseudoholomorphicity condition for minimal surfaces has been studied by various authors, e.g., Calabi [2], Chern [3], Eells and Wood [6]. For a long time, it has been known that the condition is fulfilled a priori when the surface is of genus zero and the ambient space is constantly curved. One would thus like to study the higher genus cases. Using the method of twistor lifts, and an analog of the diagonalization of the second fundamental form, Lemma 1.1, we obtain the Theorem. Let M be a closed minimal surface in a four-dimensional space of positive constant curvature k. Then M is pseudoholomorphic if \ x(TM ) \ > -2x(M), where x(M) and x(TM ) are the Euler characteristics of M and its normal bundle TM respectively. In this case, the immersion is determined up to an isometry of N by the curvature function of M. Furthermore, if k = 1 , then the area of M is an integral multiple of 2n.Note. R. Bryant [1] and Chern and Wolfson [5] showed that closed pseudoholomorphic minimal surfaces of arbitrary genus exist in S ; they called them superminimal.