The kinetics of hydrolysis of indomethacin and related compounds was studied in an alkaline medium at 25 degrees C in the presence of anionic (sodium dodecyl sulfate) and cationic (hexadecyltrimethylammonium bromide) surfactants. The rate-surfactant profiles for rate inhibition in the presence of sodium dodecyl sulfate and rate enhancement in the presence of hexadecyltrimethylammonium bromide were analyzed in terms of the current theory of micellar effects.