Study of performances on field of five Niebe varieties with trace elements supplements in Yangambi (Zaire). Response of five cowpea varieties to Mg and trace elements applied by soaking seeds before sowing was studied in field conditions at Yangambi. Neither the grain yield, nor the lipid content of grains were influenced by these elements. However, protein content of grains of all the five tested varieties was positively influenced. The increase was of up to 39 %. In the same way, Mg and trace elements positively influenced the number of seedlings and the number of attacked grains was decreased in the three new introduced varieties from the I.I.T.A./lbadan, Nigeria.