Schizophrenia is a serious psychiatric illness which is responsible for a substantial proportion of mental illness worldwide. Symptoms include hallucinations, delusions, thought disorders (related with deficits of attention, memory and executive functions) and negative symptoms like poverty of thought and emotion, and social withdrawal. For most of this century the causes of schizophrenia have been largely unknown. However, the application of new techniques in genetics, structural and functional neuroimaging, psychopharmacology, epidemiology and neurochemical are beginning to disclose the aetiology of the disorder. Recent neurochemical data show that dysfunction of central dopamine systems may mediate symptoms in schizophrenia. Traditional antipsychotics are antagonists of dopamine D2-receptors, but some of the new atypical antipsychotics appear to have different action and drugs that interact with newly discovered dopamine and neuropeptides receptor subtypes of dopamine and neuropeptides are under investigation. In this sense, we review recent findings about interactions between opioid and dopaminergic systems with a special attention directed to cortical-striate-thalamic loops that could give new data about the aetiology and treatment of this serious mental illness. Finally, cognitive and attentional deficits in animal models of schizophrenia are reviewed.