This study was conducted to determine the relative efficiency of different spiral separators and of a series of screens with oblong perforations, in the separation of cowpea (Vigna sinensis L.) seeds from soybeans. The research was conducted at the seed Laboratory of the Escola Superior de Agricultura "Luiz de Queiroz", Universidade de São Paulo, Brasil, during the year of 1979. Sixteen 1,0kg lots of Bragg, Davis, Santa Rosa, Viçoja and U.F.V. - 1 varieties were each contaminated with 100 cowpea seeds. Four lots of each variety were then processed through three types of spiral separators and in a sequential series of hand screens having oblong perforations, differing in width by 1/64-inch. Each seed lot was separated for the first time through spirals, and the accepts fraction returned two more times to produce a second and third set of accepts. The purpose of the research was to remove completely the cowpea seeds from soybean lots. The results showed that the oblong perforations were not efficient to separate cowpea from soybeans. On the other hand, the number of cowpea seeds in the accepts fraction was progressively reduced with repeated separation of this fraction, but only Rota II spiral separator removed all cowpea seeds from the soybean seed lots.