Taro (Colocasia esculenta L. Schott) is an important staple food crop in tropical and developing countries, having high water requirements. The purpose of this study was to evaluate the feasibility of using carbon and nitrogen isotopic composition (d13C and d15N) as a physiological indicator of taro response to drought, and elucidation of the relationship between the water use efficiency (WUE) under drought conditions and carbon isotope discrimination (¿13C). As an alternative to WUE determination, obtained by measuring plant growth and water loss during an entire vegetative cycle, we have used ¿13C to determine the tolerance of C3 taro plants to drought. Seven taro accessions from Madeira, Canary Islands and the Secretariat of the Pacific Community (Fiji) collections were grown under greenhouse conditions and subjected to different watering regimes during a one-year cycle. Total plant biomass (TPB), WUE and d15N were determined at the whole-plant level (WP). Corms and shoots were evaluated separately for nitrogen content (N), d13C, ¿13C and d15N. WUE showed positive correlation with TPB (r¿=¿0.4) and negative with ¿13C (r¿=¿-0.3); Corm d15N showed positive correlations with WP d15N (r¿=¿0.6) and corm N (r¿=¿0.3). Accordingly, the taro plants with enhanced WUE exhibited low ¿13C and d15N values as a physiological response to drought stress. The approach used in the present study has developed new tools that could be used in further research on taro response to environmental stresses.