Twenty seven patients with acute rheumatoid disease who had not previously received systemic corticosteroid therapy were given a pulse(s) of high dose methylprednisolone sodium succinate (MPS) intravenously. Of the 27 patients 22 received 1 g MPS once and 5 were given the drug on three consecutive days. Plasma "MP" (total MPS plus hydrolysed methylprednisolone) and cortisol levels were measured at various intervals post infusion. Clinical assessments were made before and at 2 week intervals after each infusion for 12 weeks. Patients showed objective improvement for up to 12 weeks post infusion. Maximum "MP" levels ranging between 16 and 72 mumol/l were obtained after single infusions. In a majority of the patients "MP" concentrations in plasma were reduced to values between 0.12-3.4 mumol/l in 24 h, 0.06 to 0.13 mumol/l in 48 h. Plasma cortisol levels were incompletely suppressed for a few days in all patients, but the drug was removed from plasma and normal adrenal function restored within a fortnight after steroid infusion at the latest.