The temporal sequences of acts and postures of rats during tests for isolation-induced fighting were recorded and analyzed. Scent-marking and olfactory investigation, which have been related to fighting by previous studies, were particularly emphasized. From the data a model was constructed for the sequence of behaviors which lead to and maintain isolation-induced fighting. The typical sequence begins with olfactory investigation and scent-marking; the home rat initially investigates the intruder, and the intruder initially investigates the cage. The combination of olfactory perception of a strange male and a familiar environment, it was suggested, serves to trigger an offensive mechanism in the home rat which leads to bite-and-kick attack and offensive sideways posture. The pain of the attack then triggers defensive mechanism in the intruder rat which leads to defensive upright posture and submissive posture. Whereas the functional role of the bite-and-kick attack appears to be simply the infliction of pain and elicitation of defense in the intruder, the function of offensive sideways posture as a threat behavior may be more complex. It is possible that it becomes a conditioned pain stimulus due to its close temporal pairing with bite-and-kick attack, but it is more likely that it produces defense by a process of sensitization. In any case, following the initial attack, the offensive sideways posture continues to elicit defensive behavior by the intruder even when there are no further attacks. The functional roles of the defensive postures were interpreted as positioning the intruder in such a way that the home rat cannot assume the aggressive posture from which attack is launched. Scent-marking behavior was consistent within strains, within individuals, and across different types of measures (accumulation of scent-marking marking material and performance of the stereotyped scent-marking act, crawl-over-dish). Amount of scent-marking was not correlated with attack, however, and its role in isolation-induced fighting remains unclear. In parallel to findings in other rodents, it was observed that scent-marking was diminished in animals after they had been subjected to attack.