The accumulation and disposition of the non-steroidal antiinflammatory drug isoxicam were investigated following its oral administration to 6 subjects with normal renal function and 13 patients with diminished renal function. Isoxicam was given daily as a single oral dose for 14-15 consecutive days. Steady-state plasma levels were achieved after 13 days. The effect of differences in renal function on the kinetics of isoxicam appeared to be minimal. Accumulation of isoxicam was similar in both groups of subjects and there was no significant difference between the groups in the plasma clearance or terminal half-life of isoxicam. There were substantial differences between individuals in the apparent plasma clearance and half-life of the drug, and this is reflected in the 7-fold range of steady-state plasma isoxicam concentrations encountered in the subjects.