Adolescent rats were chronically treated with alcohol, nicotine or the combination of both for 16 days. Aggression was examined before, during and following chronic treatment using the resident-intruder paradigm for anti-social behaviour. It was hypothesized that chronic alcohol consumption during adolescence will significantly heighten aggressive behaviour, whereas nicotine may have reverse effects. It was also predicted that chronic consumption of concurrent alcohol and nicotine will lead to the highest levels of aggressive behaviour. The results of the current study found no significant difference in the behaviours of the rats during baseline. However, when subjects were given alcohol alone, high doses of nicotine alone or the combination of alcohol and nicotine at either dose, aggression was significantly heightened compared to baseline. During withdrawal, a decline occurred for all groups, however alcohol alone had the strongest impact. In addition, the levels of aggression were significantly more frequent during chronic treatment when ethanol was consumed alone compared to the remaining conditions, including concurrent consumption. From the main findings of the current study it was concluded that, although chronic alcohol consumption (as predicted), increased aggressive behaviour among adolescent subjects, aggression was significantly less frequent when co-used with nicotine and when nicotine was consumed alone. Furthermore, chronic nicotine consumption at high compared to lower doses increased aggressive behaviour. These increases were not affected by the addition of alcohol. Further research is needed to determine reasons for the dose-dependent outcomes of chronically consuming nicotine alone or in combination with alcohol during adolescence.