Quinoa (Chenopodium quinoa Willd.) is a highly nutritious Andean seed crop which shows adaptability to different adverse environmental conditions. In our study, a Bolivian (Achachino) and a Danish (Titicaca) cultivar were selected to study the effects of drought. In the test regarding the effect of progressive soil drying on quinoa, soil water status was expressed as fraction of transpirable soil water (FTSW). Relative stomatal conductance (RSC), relative transpiration (RT) and relative leaf water potential (RLWP) were calculated by determining stomatal conductance, transpiration rate, and leaf water potential of the drought treated plants relative to those of fully irrigated plants. The responses of RSC, RT and RLW to FTSW were described by a linear-plateau model which allowed calculation of soil-water thresholds for stomatal conductance (C_S), transpiration (C_T) and leaf water potential (C_L) for each cultivar. Under progressive drought, Achachino showed significantly lower C_T and C_L compared to Titicaca, that is transpiration and leaf water potential were maintained in the Bolivian cultivar to a lower soil water content than the Danish cultivar. This indicates a slightly better drought tolerance of Achachino. C_S was lower for Achachino but no significant difference was found. Drought treatment showed inhibitive effects on plant growth and biomass accumulation in both cultivars.