Species-specific responses of three coastal dune plants to drought conditions were examined to investigate the causal relationship between drought tolerance and plant distribution in coastal dune regions. Measurements of net photosynthetic rates were pursued in two meteorologically contrasting years of 1989 and 1990; the summer of 1990 was characterised by long rainless periods, whereas the meteorological conditions of summer months in 1989 did not differ significantly from the average values. The reductions of net photosynthetic rates by the 1990-summer aridity differed widely among the three species. Net photosynthetic rate of Ischaemum anthephoroides, a C4 plant, distributed in hind dunes, fell to only 33% - 43% of the values in the same season in 1989. In contrast, those of Carex kobomugi and Calystegia soldanella, which were generally growing in more seaward sites, were 67% - 87% and 76% - 97%, respectively. In July 1990, Pn of Ischaemum anthephoroides were significantly lower than those of the other two species. Ischaemum anthephoroides showed the most pronounced reduction of leaf water potential as low as -2.5 MPa, while the reductions of Calystegia soldanella and Carex kobomugi remained around -1.5 and -2.0 MPa, respectively in 1990 summer period. The low tolerance of I. anthephoroides to a severe drought was correlated with shallow distribution of the root system, and is considered to be one of the reasons why the distribution of I. anthephoroides is restricted to the inland area where drought conditions are milder than in seaward areas.