Twenty-nine patients with systemic lupus erythematosus were treated with a new synthetic, unsaturated prednisolone derivative, triamcinolone, for as long as 11 months. This hormone is 1.3 times as powerful as prednisone and 4.4 times as potent as hydrocortisone as an anti-inflammatory agent. The pattern of clinical improvement closely paralleled that obtained by previous treatment with older steroids. There was a disappearance of all the clinical and laboratory abnormalities produced by the disease, with the exception of long-standing renal involvement. A major difference between triamcinolone and other steroids was a tendency, in 18 patients, toward progressive gradual weight loss, averaging 7.8 % of initial body weight. The cutaneous side-effects, particularly Cushingoid appearance, hirsutism, and striae, were more marked than those with older steroids. The most serious side-effect was muscle weakness, which appeared in six patients from 4 to 32 weeks after start of triamcinolone therapy. Fourteen patients had received prior steroid therapy with all the older anti-inflammatory hormones and seven of them were better controlled and felt better with triamcinolone than with steroids used perviously.