Diseases that are difficult to treat are central to three articles in this issue of Nature Reviews Neuroscience.

Chronic fatigue syndrome (CFS; also known as myalgic encephalomyelitis or ME) recently attracted renewed attention when a reported link between xenotropic murine leukemia virus-related virus (XMRV) and CFS could not be replicated in subsequent studies. The continuing challenge of identifying the triggers and developing treatments for this illness prompted Nature Reviews Neuroscience to invite four prominent CFS researchers to provide their perspectives on the current state and future of CFS research, focusing on neuroscience and psychiatry. Their responses can be found in the Viewpoint article on page 539.

Gliomas, the most common type of brain tumour, are another condition for which there is currently no cure. On page 495, Westphal and Lamszus discuss the recent progress in the identification of biomarkers that allow better classification of the different types of glioma, and the increasing understanding of the molecular events that switch a tumour from slow growing to anaplastic. Together, these developments provide opportunities for therapeutic intervention.

Many mental disorders that are characterized by social deficits, including autism and social anxiety disorder, are notoriously difficult to treat. The well-established role of the neuropeptides oxytocin and vasopressin in social behaviour in mammals has led to the idea that these neuropeptides and their receptors could be therapeutic targets for such disorders. In a comprehensive Review on page 524, Meyer-Lindenberg et al. consider behavioural, genetic and neuroimaging studies that have shown that the oxytocin and vasopressin systems influence human social behaviour, and discuss the results of early treatment studies in several psychiatric disorders.