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Objective Chronic lead (Pb) exposure during development is known to produce learning deficits. Nitric oxide participates in the synaptic mechanisms involved in certain forms of learning and memory. This study was designed to clarify whether Pb-induced impairment in learning and memory was associated with the changes of nitric oxide levels in mice brains. Methods Sixty Balb/c mice aged 10 days were chosen. A model of lead exposure was established by drinking 0.025%, 0.05%, 0.075% lead acetate, respectively for 8 weeks. The controls were orally given distilled water. The ability to learn and memorize was examined by open field test, T-water maze test. In parallel with the behavioral data, NO level of hippocampus tissue was detected by biochemical assay. Results Compared with control groups, (1) the weight of 0.075% group was significantly reduced (P<0.05); (2) The number of times in mice attaining the required standards in T-water maze test was lower in 0.075% group (P<0.01). No significant difference was found between experimental and control groups in open field test (P>0.05); (3) NO level of mouse hippocampus tissue was decreased in 0.075% group (P<0.01). Conclusions The findings suggest that decreased hippocampus NO level may contribute to the Pb-induced deficits in learning and memory processes. [ABSTRACT FROM AUTHOR]