Abstract
Seventy-one spontaneous thermosensitive mutants of Vesicular Stomatitis Virus were isolated and tested for complementation. The spontaneous mutation rate seems to be very high since 2.3% of mutants were found in wild-type clones. Experiments were performed at 30° (permissive temperature) and 39.8° (non-permissive temperature). The mutants can be classified into five complementation groups. 58 mutants fall into the first group.