In a water maze (WM), rats employ different and sexually dimorphic behavioral strategies to solve a place-learning task, a test of cognitive/propositional ability. Puberty is the last step in brain development and marks an important phase with regard to sexually dimorphic cognitive performance and behavior. The present study assessed possible sex differences in cognitive style before and after puberty in a WM place-learning task. Since nitric oxide (NO) is implicated in spatial learning and hippocampal function, and since brain NO2- + NO3- levels (stable metabolites of NO) display region-specific sex differences in rat brain, NO2- + NO3- levels were determined after behavioral testing. The sex-related style difference emerged very clearly but only in the adult rats, which suggests that the female behavioral strategy in the WM place-learning task requires the presence of female sex hormones at puberty. Although NO2- + NO2- levels were higher in the adult rats and males compared to prepubertal and female rats, respectively, no significant correlations emerged between brain NO and behavior. The fact that the behavioral sexually dimorphic cognitive-style effect observed here and in previous studies appears to emerge only after puberty suggests that awareness of such postpubertal sex differences may also be important in human educational and therapeutic contexts. (C) 2000 Elsevier Science Inc.