Phyhn~urinolactone (1) and phyllurine (2) were isolated from PhyUanthusurinaria L. as bioacfive substances for nyctinasty. Compound 1 was quite effective for leaf-closing of the plant at 1 x 10 -7 M in the daytime and 2 was quite effective for the leaf-opening at 2.5 x 10 -5 M, whereas beth 1 and 2 were not effec6ve for other nyctinastic plants even at I x 10 -4 M. The concentration of 1 increased before leaf-closure in the plant body, whereas that of 2 was constant through a day. Thus, the leaf-movement of P. utinaria L. is proposed to be controlled by Se change in the balance of concentration between 1 and 2, which is regulated by a ~-glucosidase, similar to the case ofLespedeza cuneata G. Don. © 1999 Elsevier Science Ltd. All fights reserved.