This report presents two-year results of investigations pertaining to the distribution and importance of caterpillar parasites of corn borer in the control of the population density of this pest in corn hybrids of different FAO maturity groups. Parasites of corn borer catepillars were the dominant factor in the control of population density of this corn pest. Particularly high efficiency in the reduction of population density of borer the parasites revealed in the region of Mionica (Yugoslavia) in 1987 in the hybrid ZP 704 (16.37% destroyed caterpillars) and in 1988 in the corn hybrid ZP 609 (14.55% parasitized caterpillars). In the region of Suvobor, the caterpillar parasites reduced the population of corn borer in 1987 by 15.13% in the hybrid ZP 663 and by 15.57% in the hybrid ZP 415, whereas in 1988 the efficiency of the parasites of borer catepillars was high in the hybrid ZP 609 (15.57% parasitized catepillars). In the experimental period, the following three species of catepillar parasites were involved in the parasitization of corn borer: Lydella thompsoni Hrt. (Diptera: Tachinidae), Campoplex alkae Ell. & Sch (Hymenoptera: Ichneumonidae) and Diadegma terebrans Grav. (Hymenoptera: Ischneumonidae). The results have shown that the most important catepillar parasite was tachina L. thompsoni since it was present in the process of parasitization of borer caterpillars in each of the hybrids studied. Approximately 50% of the L. thompsoni population in the region of Mionica managed to complete their development before law autumn temperatures became established. The higher the altitude, the larger the number of this caterpillar fly at the larval stage over winter, and the lower the number of the pupae or exuviae. This indicates that a small part of the L. thompsoni population managed to complete its development before the spell of low temperatures in autumn. Dissection of corn plants and borer caterpillars over the winter season has shown that under Yugoslav conditions C. alake and D. terebrnas both over winter at pupal stage or as first instar larvae. Other development stages of these useful insects were not registered either in corn plants or in body cavities of corn borer caterpillars. none