Plasma prednisolone levels were measured in parallel with clinical and laboratory assessments in seven patients with rheumatoid arthritis on single daily doses of prednisolone which were reduced at weekly intervals from 10 mg. to 7, 6 and 5 mg. A significant negative rank correlation was observed between prednisolone dose and the duration of morning stiffness (p less than 0.05). No significant correlation was observed between plasma prednisolone levels, other clinical assessment criteria or laboratory indices.