The intervention of Intensive Interaction is gaining attention for its demonstrated effectiveness in promoting social engagement in individuals with severe communicative impairments. The present study sought to extend the evidence base for this intervention by investigating the rapidity with which an increase in engagement becomes apparent. Videotapes of the first Intensive Interaction session for 10 adults with profound learning disabilities were microanalytically coded for four measures of engagement: eye gaze, bodily orientation to partner, proximity to partner, and emotional valence. Results showed an increase for all participants on at least two measures, while 70% of the sample showed increases on all four measures. Such shifts occurred within only a few minutes of the onset of the session (ranging from three to 14 minutes). Non-parametric analyses confirmed that this robust pattern of increases would not have been predicted to occur by chance. These findings indicate that Intensive Interaction is effective in rapidly promoting social engagement, even for individuals with a long history of apparent social avoidance. Suggestions for future lines of enquiry, at both the empirical and conceptual levels, are discussed. (Contains 2 figures, 2 tables and 1 note.)