We present the results of different communication tests on some current parallel computers, the Cray T3E and the SGI Origin 2000. The aim of this paper is to study the effect of the local memory use and the communication network exploitation on message sending. For this purpose, we have first designed experiments without network contention to establish the achievable bandwidths. We have then modified this base experiment by increasing the contention of the network and by decreasing the spatial locality properties of the messages. We analyse these results taking into account the underlying architectures and we conclude with some hints for regular applications.