Lysozyme genes have been model genes in molecular genetics. The chicken lysozyme c gene was among the first genes to be isolated and characterized, but since then, many other members of the lysozyme gene family have been isolated and characterized. Of all the members of the gene family, the conventional lysozyme c gene has been the most extensively studied at the molecular level. General properties of members of the lysozyme gene family are that they are relatively small genes of less than 10 kilobases in length, and are made up of four exons and three introns. There has been a long history of gene duplication events within the lysozyme gene family, and in several cases, eg., stomach lysozymes, this has led to the evolution of novel biological functions. Initially the structure of the lysozyme c gene appeared to support the exon theory of genes, but the recent characterization of additional lysozymes shows that the predictions of this theory are not supported. Lysozyme genes continue to yield new insights into the molecular processes moulding the vertebrate genome.