Genetic studies on C. elegans have identified genes for several nicotinic acetylcholine receptor subunits and functionally associated proteins. Analysis of viable mutants allows correlations of specific nAChR structural alterations to changes in behaviour. Molecular cloning and functional expression of C. elegans nAChR subunits permit the study of the organism's novel pharmacology and physiology. This also provides insights into the mode of action of cholinergic anthelmintic drugs, and may facilitate rational design of novel, safer animal health and pharmaceutical products. Use of the green fluorescent protein reporter gene will allow the study of the cellular localization and developmental pattern of nAChR subunit expression in an animal. Such data will be obtained in the only nervous system for which the complete cell lineage and wiring diagram is known. These studies will be pursued during the period in which the C. elegans genome sequence is completed enabling an enhanced understanding of cholinergic synaptic signalling and its regulation throughout development.