Nitric oxide has been shown to be implicated in neural plasticity that underlies processes of learning and memory. In the honeybee, studies on the role of nitric oxide in associative olfactory learning reveal its specific function in memory formation. Inhibition of nitric oxide synthase during olfactory conditioning impairs a distinct long-term memory that is formed as a consequence of multiple learning trials. Acquisition or retrieval of memory or memory formation induced by a single learning trial is not affected by blocking of nitric oxide synthase. This finding provides a first step toward dissection of molecular mechanisms involved in memory formation, in general, and the special function of nitric oxide synthase in particular.