Electrofocusing has been adapted in order to make experiments for the detection of enzyme variants more efficient. The principle of the new technique consists in making agar copies of the polyacrylamide gel by contact; the original gel and the agar copies are then developed for different enzyme systems. By doing so, the number of enzymes, i.e. loci, per test animal screened after a single electrofocusing run is increased. This method has proved to be feasible for the detection of mouse variants with altered enzyme banding patterns due to parental treatment with chemical mutagens.