This study was conducted to test whether the presence of new friends at moments of substance-use initiation differs across substances, and whether individuals tend to initiate substance use, across different substances, either with a new friend or with an old friend. Participants were 419 Italian high school students (41% female). Results showed that the presence of a new friend at the moment of substance-use initiation varied across different substances. New friends were least often present when an individual first tried cigarettes, and were most often present the first time an individual tried marijuana. Substance-use initiation in the co-presence of both an old friend and a new friend was almost exclusively linked to higher levels of substance use (marijuana and hard alcohol) and non-existent with tobacco use. However, results showed a clear tendency for individuals to initiate substance use either with a new friend or with an old friend. Results are discussed in terms of extending peer influence research to include transitions in peer relations as important moments for peer influence. (Contains 2 tables.)