The light/dark test is based on the innate aversion of rodents to brightly illuminated areas and on the spontaneous exploratory behaviour of the animals, applying mild stressors, i.e. novel environment and light. The test apparatus consists of a small dark secure compartment (one-third) and a large illuminated aversive compartment (two-thirds). The test was developed with male mice. The strain, weight and age may be crucial factors. The extent to which an anxiolytic compound can facilitate the exploratory activity depends on the baseline level in the control group. Differences between the type and severity of external stressors might account for variable results reported by different laboratories. The light–dark test may be useful to predict anxiolytic-like or anxiogenic-like activity in mice. Transitions have been reported to be an index of activity exploration because of habituation over time and the time spent in each compartment to be a reflection of aversion. Classic anxiolytics (benzodiazepines) as well as the newer anxiolytic-like compounds (e.g. serotonergic drugs or drugs acting on neuropeptides receptors) can be detected using this paradigm. It has the advantages of being quick and easy to use, without requiring the prior training of animals.