Abstract. A 3-arc is 4-touple (v,u,x,y) of vertices such that both (v,u,x) and (u,x,y) are paths of length two. The 3-arc graph of a given graph G, X(G), has the vertex set identical with the set of arcs of G. Two arcs uv and xy are adjacent in X(G) if and only if (v,u,x,y) is a 3-arc in G. We study the independence, domination and chromatic numbers of 3-arc graphs and obtain sharp lower and upper bounds for them. We also show that the problem of deciding if the chromatic number of X(G) is at most 3 is NP-complete even for planar graphs G.