Patterns in territorial defense can indicate territory functions. Encounters between introduced Sceloporus occidentalis and resident conspecifics were used to analyze patterns of response to intruders. Males tended to be more aggressive while females fled more. There was no behavioral response difference found to be dependent on the sex or relative size of the intruder. The results indicate that, for western fence lizards, territories defended during the non-mating season might function to secure material resources but not future mating rights.