Nickel deficiency was induced in 2- to 4-year-old goats by feeding 0.1 mg Ni/kg dry matter with a semisynthetic diet. The control group consumed 5.0 mg Ni/kg d.m. Activity of several enzymes (SDH, LDH, HBDH, AST, ALT, ALD, CK, CHE) was determined in the serum, liver, heart and kidneys. Serum urea-N level was also measured and transmission electron microscopic (TEM) examinations were performed. Signs characteristic of nickel deficiency (retarded growth, increased mortality of dam and offspring, parakeratosis of the skin) appeared in the low-nickel group. The activity of SDH and ALD, as well as the level of urea-N was significantly lower in the serum of Ni-deficient animals than in the control. Ni-deficient animals also had significantly lower enzyme activities in the heart (SDH, HBDH, AST, ALT, ALD and CK), liver (SDH and CHE) and kidneys (HBDH and CK). Electron micrographs showed degeneration of cardiac and skeletal muscle in the Ni-deficient animals. Ni deficiency elicited changes primarily in the heart and these resulted in depressed activity of several enzymes.