The present study aimed to analyze the biological effects induced by bioaccumulation of uranium in Phaseolus vulgaris. Ten-day-old seedlings were exposed to 0, 0.1, 1, 10, 100 and 1000 microM U in diluted Hoagland solution. Following 1, 2, 4 and 7 days' exposure, plants were monitored for uranium uptake, biometric parameters, capacities of enzymes involved in the anti-oxidative defense mechanisms (GPOD, SPOD, GLUR, SOD, ICDH, G-6P-DH), glutathione (GSH) pool and DNA integrity. Uranium contents were up to 900-fold higher in roots (31-14,916 mg kg(-1) FW following 7 days' exposure to 0.1 and 1000 microM U, respectively) as compared to primary leaves (1-16 mg kg(-1) FW following 7 days' exposure to 0.1 and 1000 microM U, respectively). Uranium exposure did not significantly affect plant growth compared to the control. For all enzymes studied, except SOD, enzyme capacities in roots were slightly stimulated with increasing contaminant concentrations (though not significantly). For roots exposed to 1000 microM U, enzyme capacities were significantly reduced. Enzyme capacities in leaves were not affected by uranium treatment. Total and reduced GSH levels were higher in primary leaves of uranium (</=100 microM U) exposed plants than in control plants. When exposed to 1000 microM U, level of total and reduced GSH dropped. These results indicate that uranium can cause oxidative stress and cellular redox imbalance. Root DNA integrity was hampered at the highest external uranium concentration. For P. vulgaris the uranium toxicity threshold is expected to be between 100 and 1000 microM U.