Plasmodium relictum (lineage P-SGS1) is a widespread malaria parasite that causes disease of different severity in different species of birds. However, experimental studies on the effects of this parasite on avian hosts are uncommon. We investigated development of this lineage in experimentally infected greenfinches Carduelis chloris and compared the obtained data with the literature information about the virulence of the same parasite lineage for phylogenetically closely related bird species. We also used an opportunity to test the efficacy of the antimalarial drug Malarone (TM) in treatment of the experimental infection. The cryopreserved strain of the lineage P-SGS1 was multiplied in 4 experimentally infected chaffinches. Light parasitemia developed in these birds; the parasites were then inoculated to 6 uninfected recipient greenfinches. Six uninfected greenfinches were used as negative controls. Light parasitemia developed in all experimental greenfinches. There were no significant effects of malaria on the body mass of greenfinches, but haematocrit value was slightly lower in experimental birds than in control ones; the infection did not cause mortality or morbidity in these birds. According to available data, all investigated fringillid birds are susceptible to P. relictum (P-SGS1), but the same malaria parasite develops markedly differently in different bird species, even closely related hosts. Thus, the observed effects of the same malaria lineage on one species of bird cannot be generalized to others, even closely related ones. The cure with Malarone (TM) was highly efficient for blood stages of P. relictum, but exoerythrocytic stages were unaffected. (C) 2009 Elsevier Inc. All rights reserved.