The existence of a continuous Z2-map from a free m-dimensional Z2-simplicial complex E to the (m - 1)-dimensional antipodal sphere S(m)-1 is characterized by means of an enumerative combinatorial criterion involving a coloring of the vertices of E. The Borsuk-Ulam theorem, 1933, and the combinatorial lemmas of Tucker, 1945, and Ky Fan, 1952, are easy consequences of this result for the case \E\ = S(m).