These experiments examined the relationship between the neurotrophic factor fibroblast growth factor 2 (FGF2) and individual differences in the expression of conditioned fear. Experiments 1 and 2 demonstrated that rats naturally expressing low levels of contextual or cued fear have higher levels of hippocampal FGF2 relative to rats that express high levels of conditioned fear and nonconditioned rats. Experiment 3 demonstrated that hippocampal FGF2 is not increased in rats that exhibit pharmacological-induced amnesia of conditioned fear. Together, these experiments provide evidence that FGF2 may be an endogenous regulator of fear responses to conditioned stimuli.