Although several animal models are used to test and screen anxiolytic and anxiogenic-like drug effects, relatively few studies have examined the effects of pharmacological manipulations in genetically selected animals for behavioral phenotypic traits more directly related to specific anxiety disorders in humans. The present study investigated the effects of a benzodiazepine midazolam in the elevated plus-maze (EPM) in two rat lines which have been selectively bred in our laboratory for high (Cariocas High-Freezing, CHF) or low (Cariocas Low-Freezing, CLF) anxiety-like traits. After being their contextual freezing response registered and compared, animals from the 24th, 25th and 26th generations of these two rat lines were exposed to the EPM under the effects of intraperitoneal injections (1.0 ml/kg) of either vehiclesaline (0.9 per cent) or midazolam in the doses of 0.25, 0.5 and 0.75. When injected with saline, CHF and CLF animals showed higher and lower anxiety-like parameters, respectively, as compared to control-animals randomly selected. Midazolam similarly increased open-arm exploration in all groups, although this anxiolytic-like effect in CLF animals only occurred at the lowest drug dose (0.25 mg/kg). These results indicate that the anxiety-like traits previously selected for high or low contextual freezing responses are also phenotypically expressed in behavioral patterns of exploration in the EPM. The usefulness of these two rat lines to model generalized anxiety disorder and screen new putative anxiolytic drug effects is explored.