Amino acid sequences for 88 distinct lysozymes c, obtained from members of four vertebrate classes and two orders of insects, are summarized. A model for the relationships and origins of major lineages within the lysozyme c superfamily-which consists of conventional lysozymes c, calcium-binding lysozymes c, and alpha-lactalbumin-is presented and supported by evolutionary analyses. Pioneering events in the discovery and sequencing of lysozymes c are traced, and salient contributions to knowledge made by sequences from various kinds of animals highlighted. A summary of the four known amino acid sequences of bird lysozymes g and an outline of the investigations on this very different kind of vertebrate lysozyme are provided. Areas of future research aimed at further elucidating early events in the evolutionary history of the lysozyme c superfamily and at understanding differences in patterns of lysozyme gene expression are outlined.