According to international consensus, dementia is defined as a gradually onset of multiple cognitive deficit centered by memory disturbances, interfering with the daily life activities and related to organic brain lesions. The diagnosis of dementia can, particularly later in stages of the disease, be made with a reasonable certainty on the basis of neuropsychological testing. Yet, neuropsychological testing is not fully quantitative and objective and it does not allow for for an objective and reproducible follow-up. For these reasons a search for biomarkers to identify and follow disease has been so actively pursued. The identification of reliable biomarkers (or surrogate markers) for dementia disorders is likely to contribute not only to a better understanding of the underlying pathophysiology, but may also work as an efficient tool to identifiy subjects at risk, for (sub)classification of disease, and to objectively monitor treatment response. With the increased prevalence of dementia with age, an aging population and the promise of disease-modifying therapies the characterization of the early stages of various types of dementia, in particular Alzheimer's disease (AD), biomarkers have become a topic of major research interest within dementia research. From human postmortem brain studies it is well documented that pronounced changes occur within several neurotransmitter system both in normal ageing and in dementia; for AD this is particularly well documented for the cholinergic transmitter system. With the new emerging techniques, including molecular imaging of the neurotransmitter systems with positron emission tomography (PET) or single photon emission tomography (SPET) the functional state of human central receptor systems brain can be assessed in vivo. When used with appropriate radioligands, PET and SPET can reveal the distribution of neuroreceptors in the living human brain, and their interactions with neurotransmitters or administered drugs. Based on previous imaging studies it seems that several– but not all - brain receptor densities decline with age but the rate of decline varies between the transmitter systems. Further, within one system the decline in density may also differ between different brain regions. These are important observations that necessitates a close matching between control and patient groups in imaging studies. In the presentation a review of neurotransmitter dysfunction in the most prevalent dementia disorders will be given. The focus will be primarily on Alzheimer's disease, but Lewy body dementia and frontotemporal dementia will also be discussed. Among the primary degenerative disorders, AD is the most extensively investigated when it comes to neuroreceptor studies. In postmortem studies marked reductions in some of the receptor systems, in particular 5-HT2 receptors, nicotinic alpha4-beta2, and a preferential loss of M2 as compared to M1 muscarinic receptors have been found. Studies of muscarinic and dopaminergic receptors have shown conflicting results. Some of these findings have been partially replicated in in-vivo imaging studies: a decrease in 5-HT2, nicotinic, and possibly muscarinic receptors. As more and more radioligands become available, neuroreceptor imaging may beome an important tool to diagnose, classify, and monitor dementia disorders.