A project for isolation of local inbred lines of corn and production of hybrid corn is being carried on since 1932 at the Instituto Agronômico de Campinas. The organization of the Hybrid Corn Service stablished in 1946 for hybrid corn seed production under supervision of the State Government of São Paulo is presented here. Basic investigation on inbred lines isolation and testing of hybrids are carried out at several Experiment Stations of the Instituto Agronômico by the Genetics and Cereals and Leguminous Plants Departments. Seed production of the required inbred lines and single crosses is made in cooperation with Federal Government at the Ipanema Exp. Sta. at São Paulo. Double cross seeds are produced in selected private farms under a contract with the Hybrid Corn Service. These seeds are stored at seven different places, where they are cleaned, classified by size, treated with DDT and conditioned in bags of 50 kg each. The hybrid seeds are sold to the farmers through the county agents of the State Extension Service. An average of 2,420 kg per hectar (about 1,500 kg of clean seeds) of hybrid seeds has been produced in the cooperative fields in the last three years. It has been estimated that about 3,000,000 kg of hybrid seeds have been produced in these cooperative fields during 1951. These amounts of seeds are used for only 1/5 of the total corn acreage in the State of São Paulo. Total corn production in this State is estimated in 1,200,000 metric tons produced in an area of about 900,000 hectars. The average cost of production of hybrid seeds in the cooperative fields in 1951 was calculated as Cr$ 1,45 per kg. The detasseling operation has been calculated in Cr$0,118 per kg of seeds (only 9% of the total cost). The most expensive operation resulted from use of chemical fertilizers, the harvesting and soil cultivation including soil erosion control. The advantages of the present organization for hybrid corn seed production in São Paulo are stressed. A similar organization for cottcn seed production is already operating in São Paulo for several years, with reasonable success.