“…We would like to mention that, as far as we know, there are a few articles on the global existence of periodic solutions for neutral differential equations, we refer to Krawcewicz, Wu and Xia [16,34,36] and Wei and Ruan [31]. Recently, several interesting articles on the stability, bifurcation theory and numerical solutions of neutral differential equations, and the fundamental theory of the neutral type differential equations and inclusions, have been published, we refer to [1,9,10,15,[25][26][27]2] and [11,13,17], respectively. The present paper is the first to study the global existence of periodic solutions of neutral differential equations by combining the global Hopf bifurcation theory of neutral equations due to Krawcewicz, Wu and Xia and the higher dimensional Bendixson's criterion for ordinary differential equations due to Li and Muldowney.…”