G-protein-coupled receptors (GCRs) are a very large protein family and are critical components in many different autocrine, paracrine and endocrine signaling systems in animals. Current estimates are that humans have several thousand GCRs encoded by only slightly fewer genes. I have developed GCRDb, a database of sequences and other data relevant to the study of the biology of the receptors. The database implementation, data collection, and query system are described. An integral component of the design of GCRDb is the classification of GCRs in families. The current composition of GCRDb is presented in a table showing the number of entries in each family and group as derived from accepted mutation parsimony analyses.