The purpose of this conference of toxicologists, geneticists, and statisticians is to increase understanding of the role of animal genetics in toxicology by discussion of one aspect of this relationship, namely the genetic structures of the laboratory animal populations used in toxicological assays. It is hoped that discussion and comparison of various attributes of inbred, F1hybrid, and outbred laboratory animal populations will result In recommendations concerning the most appropriate genetic population structures to be used to supply test animals for toxicological studies having different objectives and end points.