Lacosamide ((R)-2-acetamido-N-benzyl-3-methoxypropionamide; formerly harkoseride, SPM 927; Vimpat), has been recently approved by US and European regulatory authorities for use as add-on therapy for partial-onset seizures in adults. Because a number of anti-epileptic drugs are used to treat conditions beyond epilepsy, including anxiety, in the present study we investigated the anxiolytic potential of lacosamide in a conditioned emotional response (CER) model in rat, and the mouse marble burying assay. In each test lacosamide produced a significant effect consistent with anxiolysis, i.e. lacosamide increased suppression ratio in the CER test, and reduced the number of marbles buried in the marble burying assay. The doses necessary for an anxiolytic effect were higher than those necessary for efficacy in seizure tests conducted in the same species. For example in the mouse, the lacosamide oral ED(50) in the maximal electroshock seizure (MES) and 6 Hz tests was 5.3 and 9.6 mg/kg respectively, and the minimal effective dose in the marble burying assay was 30 mg/kg. In both seizure and anxiety tests, the (S)-enantiomer of lacosamide was inactive suggesting a similar mechanism of action, possibly use-dependent inhibition of sodium channel function (Errington et al., 2008). Efficacy in the CER model was equivalent to diazepam and pregabalin (Lyrica). In tests of side-effects, lacosamide had no effect on choice accuracy in the delayed match to position task of working memory, although at the 30 mg/kg dose, response rates and response latencies were significantly affected. In sum, the present results identify for the first time, an anxiolytic potential of lacosamide.