Nicotinic acetylcholine receptors (nAChRs) are excitatory neurotransmitter receptors with important roles in both vertebrate and invertebrate species. Mammalian and insect neuronal nAChRs have attracted considerable attention as target sites for drug and insecticide development. Human neuronal nAChRs have been implicated in several neurological disorders and, in addition, insect nAChRs are target sites for commercially important insecticides which are used extensively in animal health and crop protection applications. Nicotinic receptors display considerable heterogeneity in their subunit composition (17 different nAChRs subunits have been identified in vertebrates and about 10 subunits in insect species). Heterologous expression of nAChRs subunits cloned from mammalian and insect species has helped to establish the influence of nAChR subunit composition upon pharmacological and functional properties. A major goal for both drug discovery and insecticide development is the identification of subtype-selective compounds. We have employed radioligand binding and electrophysiological approaches to examine the pharmacological properties of recombinant nAChRs. The importance of subunit composition and the influence of subunit domains have been examined by the expression of hybrid receptors, artificial subunit chimeras and by site-directed mutagensis. These approaches are currently being used to characterise a variety of nicotinic agonists, antagonists and potentiators. For example, recent studies of mammalian nAChRs have identified amino-acids important in determining subtype-selective and species-selective potency of novel nAChR agonists and revealed their importance in the coupling of binding to channel gating. Neonicotinoid insecticides, which act on insect nAChRs, have been used extensively for crop protection and animal health applications since their introduction in the early 1990s. Compared to some other insecticide groups, resistance to neonicotinoids has been slow to develop but is now established in field populations of certain insect pests. We have reported recently the identification of a resistance-associated target-site mutation (Y151S) within two nicotinic acetylcholine receptor (nAChR) subunits (Nlα1 and Nlα3) from the brown planthopper Nilaparvata lugans, a major rice pest in many parts of Asia. The influence of this mutation upon the functional properties of recombinant nAChRs has been examined by heterologous expression in Xenopus oocytes and a cultured Drosophila cell line. The Y151S mutation was found to have no significant effect on the maximal current observed with the endogenous nAChR agonist acetylcholine. In contrast, a significant reduction in maximal current and a rightward shift in agonist dose-response curves was observed for all neonicotinoid compounds. Interestingly, substantial differences were observed in the magnitude of these effects with different neonicotinoid compounds examined.