A high-pressure liquid chromatographic method is presented for the determination of ibuprofen in human plasma. Ibuprofen is extracted from plasma acidified with 1.0 M phosphoric acid using hexane containing p-phenylphenol as an internal standard. A reversed-phase octadecylsilane column was used with a liquid phase of 65% methanol and 35% 0.10 M acetate buffer (pH 5.0). A spectrofluorometric detector with an excitation wavelength of 253 nm and a band pass filter (230--420 nm) provided a detectable peak for 1 microgram of ibuprofen/ml of plasma. The effect of the pH and molarity of the mobile phase on the capacity factor was studied.