Luteolin, isolated from the seeds of Perilla frutescens (perilla seeds), inhibited the peroxidation of linoleic acid catalyzed by soybean lipoxygenase-1 (EC 1.13.11.12, Type 1) with an IC(50) of 5.0 M (1.43 μg/mL) noncompetitively. The progress curves for an enzyme reaction indicate that luteolin shows slow binding kinetics. Both the initial velocity and steady-state rate in the progress curve were decreased with increasing the concentration of luteolin. The kinetic parameters, which described the inhibition by luteolin, were evaluated by nonlinear regression fits.