The pathogen of american bovine trypanosomiasis Trypanosoma vivax was transmitted between zebu bull calves by blood meal interruption and immediate resumption of female Tabanus importunus horse flies. Transmission was achieved by 44 transfers from the donor animal to the recipient animal carried out from 8 to 10 days after experimental inoculation of the donor animal. Parasitemia was detected in the recipient animal 10 days after transfer beginning.