This study was carried out to determine the effect of water stress on five different generative stages of soybeans and to evaluate the CROPGRO-soybean model under semi-arid climatic conditions. The study was conducted at the Faculty of Agricultural Engineering, Harran University research field in 2003 and 2004 growing seasons. Plants received full irrigation during vegetative stages, after which it was cut off at different reproductive stages (treatments): R1-2, beginning of flowering and full bloom; R-3, beginning of pod; R-4, full pod; R-5, beginning of seed; and R-6, full seed. The control treatment was full irrigation throughout. Observed yields ranged from 1955 (R6) to 3684 kg ha(-1) (control) in 2003, and from 1867 (R-6) to 3952 kg ha(-1) (control) in 2004, respectively. Generally, in both of the years any water stress imposed on soybeans in three different generative stages (R-3, R-5, and R-6) resulted in substantial yield reduction compared with full irrigation; yield reduction was greatest at the R-6 stage. Biomass and 1000 seed weight also showed significant difference. Overall, CROPGRO-soybean simulated parameters from all treatments were higher compared with observed ones. Although simulated yield results were close to measured ones, they could not track observed yield patterns. Generally, the CROPGRO-soybean simulation model failed to satisfactorily mimic observed soybean yield, biomass, and 1000 seed weight and therefore it is suggested not to be used for similar scenarios and climatic conditions. (c) 2007 Published by Elsevier B.V.