Details of receptor structure and function that were unavailable as recently as two years ago are now readily obtainable through the application of molecular biological techniques. Cloning and sequence analysis of neurotransmitter receptor genes have provided information on the primary structure of these proteins, revealing the relationship between pharmacologically diverse families of receptors. Knowledge of the primary structure of receptors has allowed for prediction of secondary structure and the construction of three-dimensional models. Permanent expression of cloned neurotransmitter receptor genes in cultured cells is providing unlimited sources of pure receptor, which allows for pharmacological and biochemical studies on single receptor subtypes. The use of site-directed mutagenesis to elucidate the relationship between protein structure and function has provided considerable information on the role of certain conserved amino acids in receptor function and has suggested possible molecular mechanisms of signal transduction across membranes. The article will review some of these recent developments in the area of neurotransmitter receptors and point out the utility of molecular biology in these endeavors.