Universal Class III PI3-K ELISA kit offers activity level determination of Class I, Class II and Class III enzymes. A simple and sensitive method is provided for PI(3)P quantification in a 96-well format. It is a competitive ELISA, in which the signal is inversely proportional to the amount of PI(3)P produced. After the PI3-K reactions are complete, reaction products are added to the PI(3)P-coated microplate for competitive binding to a PI(3)P detector protein. The amount of PI(3)P detector protein bound to the plate is determined through colorimetric detection.