In spite of a lack of acute toxicity of single metal ions, in 96 hour laboratory tests there was a long term toxicity against S. carpocapsae and H. bacteriophora nematodes. The 96 hour laboratory tests were carried out in order to prove possible synergistic and antagonistic interactions between pairs of metal ions. Thus, the pairs of ions were arranged from each of Al, Cd, Co(II), Cr(III), Cr(VI), Cu(II), Fe(III), Li, Mo(VI), Ni(II), Se(IV), V(V) and Zn on one side and Mn(I1) and Mg on the other. Mn(I1) and Mg ions considerably reduced the nematode mortality and increased their infectivity against Galleria mellonella caterpillars.