A single dose pharmacokinetic study was conducted on two sustained-release formulations (75 mg) of indomethacin (Indocid capsules 'A' and Indogesic tablets 'B'). The study was carried out on 22 healthy male volunteers, who received a single oral dose (75 mg) of each product according to a randomized crossover design. Blood samples were obtained over a 24 h period, and drug concentrations were determined by an HPLC assay. The two products were not found to be statistically different with respect to the lag time between dosing and first appearance of the drug in the serum (1.0 +/- 0.1 and 0.9 +/- 0.1 h for A and B, respectively), or in the time needed to attain the peak concentrations (3.3 +/- 0.3 and 3.3 +/- 0.5 h for A and B, respectively). The two products, however, varied significantly in the peak serum concentrations (2721 +/- 220 and 1797 +/- 129 ng/ml for A and B, respectively). In terms of the extent of absorption, assessed by estimating the area under the concentration-time curve over 24 h, the two products were not found to be significantly different (11,575 +/- 630 and 10,212 +/- 556 ng . h/ml for A and B, respectively). Based on these findings, the two formulations can be considered bioequivalent in the extent but not in the rate of drug absorption.