Tsoucas, P.Walrand, J.Monotonicity of throughput is established in some non-Markovian queueing networks by means of path-wise comparisons. In a series of DOT/GI/s/N queues with loss at the first node it is proved that increasing the waiting room and/or the number of servers increases the throughput. For a closed network of DOT/GI/s queues it is shown that the throughput increases as the total number of jobs increases. The technique used for these results does not apply to blocking systems with finite buffers and feedback. Using a stronger coupling argument we prove throughput monotonicity as a function of buffer size for a series of two DOT/M/1/N queues with loss and feedback from the second to the first node.en-USTechnical Report