Conventional glucocorticoids exert a negative influence on calcium balance, and long-term treatment with these agents leads to osteopenia. Deflazacort is an oxazoline derivative of prednisolone with documented calcium-sparing properties when compared to prednisone on a weight basis. The purpose of the present study was to determine the relative antiinflammatory potency of deflazacort and prednisone. In a randomized, cross-over, double-blind trial, 11 patients, all suffering from polymyalgia rheumatica, and all on a stable maintenance dose of prednisone, were treated with equimolar doses of prednisone and deflazacort (i.e., weight ratio 1:1.2) for two consecutive 2-week periods. Following deflazacort treatment, significant rises compared with initial values were seen in erythrocyte sedimentation rate (ESR), plasma fibrinogen, serum alkaline phosphatase, and general pain and tenderness. No changes were seen following prednisone treatment. Subsequently, in a similar regimen, prednisone was compared with deflazacort at a weight ratio of 1:1.2 in 10 patients, 1:1.5 in another 10 patients, and 1:1.8 in still another 10 patients for purposes of dose titration. Again, significant rises were seen in ESR, plasma fibrinogen, and serum alkaline phosphatase following the lowest dose of deflazacort, whereas no changes were seen following the higher doses of deflazacort or prednisone. In conclusion, the relative antiinflammatory potency of deflazacort and prednisone lies between 0.83 and 0.66 on a weight basis (1.02 and 0.82 on a molar basis) as evaluated by clinical and biochemical parameters reflecting disease activity in polymyalgia. This disease appears to represent a sensitive, reliable and reproducible clinical model for assessment of the relative antiinflammatory potency of glucocorticoids.