Selected plants used to treat susto, a folk illness recognized by various groups of Latin America, were screened for anxiolytic and/or fear suppression activity in behavioral assays. We found that the plant used by most of the healers interviewed (Adiantum tetraphyllum Humb. & Bonpl. ex Willd.; Adiantaceae) suppressed certain components of anxiety and fear. To our knowledge, this is the first report on the biological activity of Adiantum tetraphyllum. This finding supports the contention that susto may represent what in the Western culture is defined as fear or anxiety, and hence may share the same psychological, biological or neural underpinnings. In light of the available literature, this represents the first experimental investigation of the biological activity of plants specifically in the perspective of their use in treating a culture-bound syndrome.