The aim of this trial was to quantify the variation in growth and lamb meat quality between entire male and castrated male lambs reared under traditional grass systems, and to identify the possible problems in rearing mixed sex groups together. Much work has been carried out on the effects of castration on meat quality and growth (Butler-Hogg et al. 1984; O' Riordan and Hanrahan, 1992), and on pelt removal (Andersen et al.; 1991a, 1991b); this experiment set out to ascertain whether entire male lambs would finish quicker than wether lambs off average condition grass swards in a semi-commercial situation and therefore to determine the necessity of castrating lambs that will be finished by September.