Bigenic APPswe + PS1/ΔE9 mice with Aβ plaque formation in neocortex and hippocampus were evaluated in three tests measuring exploratory activity. By comparison to a non-transgenic group controlled for age and gender, 7-month-old APPswe + PS1/ΔE9 mice spent more time in the open arms and had higher open/total entries and duration in the elevated plus-maze, indicative of disinhibitory tendencies. On the contrary, the groups did not differ in T-maze and open-field tests. Moreover, the motor coordination of the bigenic group was equivalent to that of controls in stationary beam, coat-hanger, rotorod, and grip strength tests. No mouse displayed neurological signs, such as pathological reflexes, myoclonus, or convulsions. The results in the elevated plus-maze test are akin to the loss of inhibitory control observed in some patients with Alzheimer's disease.