This study was conducted at the Soybean National Research Center, EMBRAPA and Instituto Agronômico do Paraná, IAPAR, Londrina, Paraná, Brazil, to determine the effects of preharvest desiccation and antecipated harvest, on soybean seed quality. Seed fields of soybean, cultivar Davis, were sprayed with the desiccant ?Paraquat? at rate of 2,0 l/ha, during 1978/79, 1979/80 and 1980/81 seasons. In the last season, it the behavior of the product ?Bromoxinil? as a desiccant at rate of 1,0 l/ha was also studied. Two harvest dates were performed: the first when the seed moisture content ranged from 17% to 18%; and the second, considered by farmers, as the normal harvest date, with the moisture level of 13%. After the first harvesting date, seeds were dried in ventilated bins with non-heated air. For the last two years of study, the desiccation resulted in a four day harvest antecipation m relation to the normal date. For the first year a nine day interval occurred between each harvesting dates. Seed quality was evaluated by germination tests, accelerated aging, as a vigor test, and fungi biossay test. Vigor level of seed treated with desiccants was slightly superior than seed harvested at the normal date. Meanwhile, for the germination results, such differences were yet smaller. Fungi biossay tests were only conducted on seed harvested at 1980/81. The results showed a non-significant effect of microorganisms on seed quality, probably due to favorable climatic conditions during the seed maturation phase. Nevertheiess, ?Paraquat? treated seed showed a slightly better index of healthy seed than non-treated and Bromoxinil treated seed. It is suggested not to use preharvest desiccants on soybean seed producing fields, in places with similar climatic conditions to Londrina, State of Paraná. This is due to the little improvement obtained in seed quality, and also to great number of risks and disadvantages of such practice.