Out of five complementation groups of vesicular stomatitis virus (VSV) type Indiana, each represented by two temperature-sensitive (ts) mutants, only representatives of group V showed genetic complementation by avian myeloblastosis virus Pseudotypes (AMV); the VSV (AMV) appeared among the progeny. Thermolabile (tl) mutants with apparently defective glycoprotein were phenotypically stabilized by growth in the presence of AMV, but a tl mutant with a defect in some other structural protein was not. Mutants with a tl glycoprotein and a ts defect corresponding to complementation group I were phenotypically stabilized by growth in the presence of AMV, but did not show genetic complementation by AMV.