In conclusion, we have found that honokiol (1), a simple biphenyl lignan, isolated from the bark of medicinal plant Magnolia species, can effect significantly neurite extension as well as neuronal survival in the primary cultures of rat cortical neurons. Honokiol appears to exert neurotrophic effects on neuronal cells and to affect neurite outgrowth. Although honokiol has been known to exhibit a numberof biological activities related to CNS, 6 there is no report on neurotrophic activity of honokiol. Honokiol shows an anxiolytic-like activity in vivo, 18 and recently GABAA receptor was reported to be involved in this activity mediated by honokiol. 19 In addition, activation of GABAA receptor by the treat- ment of honokiol plays an important role in a variety of CNS related activities, 20 and thus trophic actions induced by honokiol are presumably closely related to GABAA receptors. Our studies along this line are now under way to clarify neurotrophic effects of honokiol.