The Berenice-78 strain of T. cruzi is very different from the Berenice strain isolated 16 years earlier from the same pacient. The authors verified is high infectivity and low virulence for C3H inbred mice that survived the acute phase of infection. In these animals, it was verified that the tropism of parasites was more accentuated for cardiac and skeletal musculature and the parasitaemic level progressively increased with sucessive blood passages with posterior stability.