Rumination-like behavior, or merycism, of 5 adult male koalas (Phascolarctos cinereus) with various degrees of tooth wear was investigated using acoustically sensitive radio telemetry. Increased tooth wear was associated with a significant increase in mean rate of merycism mastication, mean number of merycism mastications per bout per 24 h, and mean number of mastications per 24 h. The ratio of mean number of ingestive mastications to mean number of merycism mastications per 24 h remained approximately 17:1 with increasing tooth wear. These results suggest that in contrast to true rumination, alterations in merycism behavior may be important in compensating for reduced molar effectiveness.