 Approximately one third of patients with schizophrenia show a poor response to standard treatment with antipsychotic medications. This treatment resistant group of patients represents a major challenge in everyday psychiatry, and consumes a disproportionate amount of time from the clinicians, resulting in considerable costs to the society and government. Anecdotal evidence suggests that the enzyme dipeptidyl peptidase IV DPPIV may be altered in patients with schizophrenia, with a higher level DPPIV enzyme activity being noted. We postulate that this may play a role in the neuropathology of schizophrenia patients and by inhibiting the DPPIV enzyme activity with a DPPIV inhibitor such as linagliptin, we will be able to improve and even ameliorate the symptoms of schizophrenic patients. However, until now there have yet any studies on the potential of these inhibitors in schizophrenia patients. A pilot study is thus proposed to evaluate the potential of the DPPIV inhibitor, linagliptin as an adjunct in schizophrenia patients who are non-responsive to treatment, which will establish the feasibility of a larger trial. 