Behaviour of viruses and salmonellas in ticks after their single or combined contamination was thoroughly studied on laboratory animals with bacteriemia or virusemia. When Ixodes ricinus was contaminated simultaneously with forest-spring encephalitis virus and saimoneilas there were observed a decrease in the virus titer by the 30th-40th days and its death in 60 days. In case of the I.ricinus nymphs contamination, the virus titer after the combined contamination was by a factor of 102 lower in 60 days vs. the contamination with the virus alone and did not reach the contamination dose. The simultaneous contamination of the ticks with two pathogens (forest-spring encephalitis virus and saimoneilas) resulted in inhibition of the growth and development of both the virus and the saimoneilas.