An event communication algorithm for efficient exchanges among parallel logic simulations, which avoids deadlock messages, is proposed in this paper. The parallel logic simulator is realized in a cluster of computers connected to a network. The effectiveness of the proposed communication algorithm is evaluated by its application to benchmark circuits. The proposed communication algorithm is called event clumping. In event clumping, the events are stored in the buffers of the output subcircuits assigned to each computer. In the case that the conditions for message release are satisfied, the events inside the buffer are packed and transmitted as one message. In event clumping, not only does it become possible to reduce the number of messages, but the null messages can be eliminated inside the buffer, which is required in order to avoid deadlocks. In the case of eight connected personal computers, the evaluation results of application to benchmark circuits showed that the number of messages and null messages decreased to about 0.1% and 1.3%, respectively. The possibility of 9.2-fold improvement in one-computer capabilities is also indicated. © 2000 Scripta Technica, Syst Comp Jpn, 31(8): 5967, 2000