The pathogenicity of several isolates of Botrytis cinerea resistant in vitro to fludioxonil and vinclozolin was tested on green tomato fruits and on tomato stems. Some isolates lost their pathogenicity, but most of them were still able to infect tomato. Back isolates were found to be still resistant to the fungicides, demonstrating that a high level of resistance may not be bound with a loss of pathogenicity. The fitness of these strains in the field remains to be proved. The same results were obtained with the laboratory strains of Sclerotium cepivorum.