The purpose of this grant funded investigation was to examine the impact of friendship alliance in an early adolescent population on cigarette and alcohol variables. Sixth, seventh and eighth grade students from two urban areas completed a survey that addressed cigarette and alcohol attitudes, practices, expectancies and intentions. Only those students who had active written consent from parents or guardians participated in the investigation. The sample consisted of 847 sixth graders, 857 seventh graders, and 493 eighth graders. Each early adolescent reported the gender of their best friend and best friend alliances were grouped into boy-boy, girl-girl, or boy-girl best friends. Results indicated most early adolescents were engaged in same-sex best friendships but that there were a small group of cross-sex best friends. There was also a small group of individuals who changed the gender of their best friends over the three years of the study. The number of cross-sex best friends increased slightly from 7.7% in sixth grade to 10.8% in eighth grade. A cross-sex best friend alliance during early adolescence was significantly related to holding more positive expectancies toward both cigarettes and alcohol, having a non-smoker accept a cigarette from a best friend in sixth grade, and having a non-drinker accept an alcoholic drink from a best friend in seventh and eighth grades. For all early adolescents, the perception that their best friend smoked was significantly related to their own positive attitude toward cigarettes and the likelihood that they smoked. Findings from this report have shown the usefulness of breaking the peer influence variable of best friendship into three different friendship alliances. By analyzing the friendship alliances individually, factors associated with peer influence on cigarette and alcohol expectancies, intentions and use can be identified in order to make substance use prevention programs more meaningful. [Appended is: (1) Questionnaire Items Used for Data Analysis in Current Investigation.] (Contains 5 tables.)