Thirty-six rams of Chokla breed of about 1–1½12 years of age were randomly divided into six groups and were fed for 4 months on a basal ration of Cynodon dactylon grass or its hay ad libitum. One group acted as the control, while the rations of the remaining groups were respectively supplemented with 250 g of a concentrate mixture, 250 g of lucerne hay, mg CoCl2.6H2O, 10 mg CuSO4.5H2O and 1 mg CoCl2. 6H2O plus 10 mg CuSO4. 5H2O per animal per day. The mean copper, sulphur and cobalt ingestion in the different groups respectively ranged from.1 to 9·7, 475 to 2030 and 0·10 to 0·53 mg per animal per day. The copper, sulphur, fibre diameter, staple length, medullation percentage, crimp per cm and staining grade were not significantly (P > 0·05) affected by the different dietary treatments. The wool copper was strongly correlated with wool sulphur (r = + 0·79) and both were inversely correlated with fibre diameter and medullation percentage. Wool sulphur, but not wool copper, was inversely correlated with staple length. Wool copper, but not wool sulphur, was inversely correlated with the staining grade of canary coloured wool. Staining grade was inversely correlated with fibre diameter as well as crimps per cm. The results suggest that copper plays an intrinsic role in the marshalling of the sulphur component of wool and in the synthetic mechanism of the wool fibre. A suggestion has been made that copper may be playing a biochemical part in the physiological processes causing canary coloration in Indian wools.