Water fluxes and daily energy expenditure (DEE) of Gallotia galloti, G. stehlini and G. atlantica, were estimated over a three-year period using the doubly-labelled water (DLW) method. Water influx varied little between seasons and between sexual categories. Juveniles tended to have higher water fluxes in spring in all three species; after a dry period the water turnover tended to decrease for all sexes in G. galloti and G. stehlini, whereas little variation was observed for G. atlantica. The average water influx, combined for all periods, was 46.27, 50.97 and 38.20 ml H2O.kg-1 d-1 for the three species respectively; only the last value differs significantly from the remaining two. The mean DEE, for all periods combined, were 189.7, 179.4 and 146.5 J g-1 d-1 for the three species respectively. As for water turnover, only the value for G. atlantica differed significantly. These data suggest that: G. atlantica may be better adaptated to maintain homeostasis during dry periods and that differences in interspecific DEE can also be explained by others factors than differences in habitat, climatic conditions, daily profiles of activity or body temperatures. We suspect that the incidence of intraspecific competition has more importance in G. atlantica than in the two other species.