Passiflora incarnata L. (Passifloraceae) is important in herbal medicine for treating anxiety or nervousness, Generalized Anxiety Disorder (GAD), symptoms of opiate withdrawal, insomnia, neuralgia, convulsion, spasmodic asthma, ADHD, palpitations, cardiac rhythm abnormalities, hypertension, sexual dysfunction and menopause. However, the mechanism of action is still under discussion. Despite gaps in our understanding of neurophysiological processes, it is increasingly being recognized that dysfunction of the GABA system is implicated in many neuropsychiatric conditions, including anxiety and depressive disorders. Therefore, the in vitro effects of a dry extract of Passiflora incarnata (sole active ingredient in Pascoflair® 425 mg) on the GABA system were investigated. The extract inhibited [(3) H]-GABA uptake into rat cortical synaptosomes but had no effect on GABA release and GABA transaminase activity. Passiflora incarnata inhibited concentration dependently the binding of [(3) H]- SR95531 to GABA(A) -receptors and of [(3) H]-CGP 54626 to GABA(B) -receptors. Using the [(35) S]-GTPγS binding assay Passiflora could be classified as an antagonist of the GABA(B) receptor. In contrast, the ethanol- and the benzodiazepine-site of the GABA(A) -receptor were not affected by this extract. In conclusion, the first evidence was shown that numerous pharmacological effects of Passiflora incarnata are mediated via modulation of the GABA system including affinity to GABA(A) and GABA(B) receptors, and effects on GABA uptake.