Reward-seeking behaviors depend critically on dopamine signaling--dopamine neurons encode reward-related information by switching from tonic to phasic (burst-like) activity. Using guinea pig brain slices, we show that nicotine, like cocaine and amphetamine, acts directly in striatum where it enhances dopamine release during phasic but not tonic activity. This amplification provides a mechanism for nicotine facilitation of reward-related dopamine signals, including responses to other primary reinforcers that govern nicotine dependence in smokers.