Male frogs of most species produce few and stereotyped calls. However, a few species exhibit a more sophisticated calling behaviour. We studied the calling behaviour of the treefrog Polypedates leucomystax in the field in Western Thailand. Male frogs were calling with a low spontaneous calling rate (less than 3 calls/minute in isolated males) with an irregular temporal patterning of the calls. Call diversity was very high; nine different call notes and 3 stereotyped combinations were recorded. The number of calls and call diversity increased in response to playback. During male-male interactions the entire call repertoire was produced. Therefore, most of this call repertoire is probably used in male-male interactions as an acoustical display. Interestingly, the latency between stimulus and response depended categorically on call type. Some of the call types believed to be aggressive calls followed a playback stimulus with latencies below 1 s, but other call types follow the stimulus with long latencies. It is unlikely that the short response latencies function to avoid call overlap, since calling is infrequent and random. Instead, short response latencies probably reflect increased levels of aggression directed towards the first caller. Thus, response latency itself may have signal function in this frog species.