The pharmacokinetic parameters and relative availability of niflumic acid in two different pharmaceutical preparations were studied in 12 subjects after a single oral administration. Total plasma clearance averaged 45 ml/min, and the half-life of elimination approximately 2 h, giving a distribution volume of 0.12 l/kg on the average. The values of these pharmacokinetic parameters were in agreement with the general characteristics of this type of substance, a weak acid strongly bound to plasma proteins. Comparison of the systemic availability of the two oral forms showed no difference; they were probably close to 100%.