An investigation has been made of the general relationships governing the epoxidation of butadiene by organic hydroperoxides (TAHP, TBHP, IPBHP, EBHP) with catalysis by molybdenyl propylene glycolate, and a detailed study has been made of the kinetics of the reaction for tert-amyl hydroperoxide. A mathematical model of the process has been developed, adequately describing the experiment with variation in [TAHP](0) from 0.5 to 1.5 mole/l and in [Cat](0) from 3 to 8 x 10(-4) mole/l at a temperature of 110 degrees C, and taking account of the change in activity of the catalyst as a function of [Cat] and [ROOH](0). The complex influence of additions of an alcohol, which inhibits the epoxidation rate, but at the same time increases the proportion of the active form of the catalyst, has been explained. The generality of the effects observed for all the examined reactions of hydroperoxide oxidation has been confirmed, and also the need to allow for change in the state of the catalyst in the solution during modelling of these processes.