Leishmania (V.) braziliensis, the causative agent of mucocutaneous leishmaniasis in the New World, may present an LD1 type genomic amplification that appears as a small 245 kb linear chromosome, and is not clearly associated to the presence of a selection agent. A bt1 gene, codifying for a biopterin transporter protein, was identified in this small chromosome. Leishmania are auxotrophic for pterins and one of the proposed explanations for the appearance of this amplification is the improvement of biopterin capture by the parasite. We analyzed some biological aspects of two lineages of L. braziliensis strain M2903, with and without the small amplified chromosome. We showed differences in infectivity of these lineages, in macrophages and the insect vector Lutzomyia longipalpis, as well as in the uptake and metabolization of intermediates of the Leishmania biopterin salvage pathway. Our results suggest that the genomic amplification favors survival due to improved biopterin capture and at the same time hinders the infective capability, suggesting that within a population different parasites can perform different roles. (C) 2009 Elsevier Inc. All rights reserved.