This publication contains the proceedings of a seminar held in Toulouse, France, on 10th, 11th and 12th June 1980, under the auspices of the Commission of the European Communities, Directorate General for Agriculture, Division for the Coordination of Agricultural Research, as part of a programme of research on beef production. The seminar was intended to bring together available experience on the utilisation of hereditary muscular hypertrophy for meat production in the member states of the European Communities. Although the phenomenon of double muscling has been exploited in various countries, particularly France, Italy and Belgium, different breeds are used and different methods of exploitation employed. An attempt was therefore made to bring together the collective experience of participants. Contributions ranged from those on the inheritance of muscular hypertrophy to alternative production systems and from fundamental studies of muscle growth to practical ways of selling the additional musrile found in animals with muscular hypertrophy. The collection of assembled papers and discussions thus represents one of the most extensive reviews of the subject that has been attempted.