 The study will comprise two dosing periods in two different cohorts of healthy volunteers. The investigators will begin with a single dosage period I 1 injection of 25 mg of Risperidone for each subject; single dosage period II, different from the previous one 1 injection of 37.5 mg of Risperidone for each subject, in a second group of healthy volunteers different from the first group will not start until after a preliminary analysis has been made of the safety data and plasma concentration data are known for the formulation of prolonged release Risperidone using the ISM technology. 