The self-ignition (SI) limit is the lowest concentration of a pyrophoric compound in solution with a hydrocarbon solvent that will ignite spontaneously when brought into contact with air. A simple quantitative method for measuring the SI limits of pyrophoric compounds is described. The SI limits are given for the aluminum alkyls triethylaluminum (TEA), diethylamminum hydride (DEAH) and trimethylaluminum (TMA) in a series ofn-hydrocarbons at 20°C. The results indicate pyrophoric reactivity increases in the order TEA, DEAH, TMA. The hexane SI limits of TMA/TEA mixtures are also given, and are shown to vary nonlinearly with pyrophoric composition.