Although impaired joint attention is one of the core clinical features of pervasive developmental disorder including autistic disorder and Asperger's disorder, experimental studies failed to report its impairment. This discrepancy might be the result of differences between real-life and experimental situations. The present study examined joint attention in 11 individuals with Asperger's disorder and 11 age-matched controls under naturalistic conditions using a target detection paradigm with dynamic emotional gaze cues. Although both groups showed gaze-triggered attention orienting as assessed by the differences in reaction time for invalid minus valid cues, enhancement of joint attention by fearful (vs. neutral) gaze was observed in the control, but not in the Asperger group. This suggests that the integration of emotion and gaze direction that elicits strong joint attention is impaired in individuals with Asperger's disorder. (Contains 2 tables and 2 figures.)