Secondary copper deficiency in ruminant animals is induced by high dietary levels of molybdenum (Mo), iron (Fe) or sulphur (S). Within the rumen, sulphur reacts with Mo to form a series of thiomolybdate molecules (TM) which may chelate copper. This reduces copper absorption or if TM is absorbed, inhibits copper metallo-enzyme activities. Parental administration of TM has resulted in an increase in Cu to the brain and an increase in Mo to the pituitaries (Haywood et al., 1998). This redistribution may alter neurological, endocrine and reproductive function. However, there are no reports on effects of endogenously produced TM on brain or pituitary trace element accumulation. The objective of this study was to determine the effect of dietary Mo or Fe on copper status and mineral retention in the pituitary gland and ovary of growing lambs.