The isolation of substance P (SP) in 1931, and the later discovery of its preferred neurokinin (NK)1 receptor, led to an intense research effort aimed at elucidating the biological role of SP, particularly within the central nervous system. There is now a large body of evidence to support the hypothesis that SP is one of the most important neurotransmitters and neuromodulators present in the brain. Its pharmacology has been intimately linked to the pathophysiology of several relevant neurological and psychiatric disorders, namely nociception, migraine, asthma, nausea, inflammatory bowel syndrome, urinary incontinence, anxiety and depression. This wide therapeutic potential triggered an unprecedented research effort, both preclinically and clinically, to identify appropriate NK1 receptor antagonists and transform them into effective drugs. To date, despite huge investments made by some of the largest pharmaceutical groups worldwide, aprepitant (MK-869, an anti-emetic agent) remains the only NK1 receptor antagonist on the market. Nevertheless, the 'NK1 receptor antagonist race' is not over, as witnessed by the significant number of patents and scientific publications claiming the discovery of new NK1 receptor antagonists issued in recent years. This review describes the most relevant results obtained in this field in the period 2005 to 2006.