 Athlatoxin B1 AFB1 is a common contaminant of poultry feed in tropical and subtropical regions. It has been shown to cause adverse effects on bird health, but recent research suggests that even low levels can negatively impact broiler performance. This is further complicated by differences in study design, including type of birds and duration of exposure. Additionally, there is limited information available about the effects of AFB1 on the gastrointestinal tract, which is an important area for future investigation. Finally, new hypotheses regarding the metabolism of AFB1 and its possible biphasic effects on broiler performance are discussed. This article was authored by Joseph Bohm, Ebrahim Razazzi-Fazelli, and Aga W. Unis.