Abstract
The trypanocidal drug ethidium bromide induced abnormal circular DNA molecules with high frequency in the kinetoplast of Trypanosoma cruzi. These molecules are circular dimers, trimers, or higher circular forms with a contour length which is a multiple of the monomer length usually found in the kinetoplastic DNA of normal trypanosomes. These abnormal molecules represent more than 30 per cent of the kinetoplastic DNA, while in normal kinetoplastic DNA we only observed three circular dimers out of several thousand molecules measured.