The susceptibility of wild-caught European passeriform birds to naturally isolated malaria parasites, Plasmodium (Novyella) nucleophilum and Plasmodium (Novyella) vaughani, was studied by means of intramuscular subinoculation of infected citrated blood. Plasmodium nucleophilum of the great tit, Parus major, was transmitted to 3 great tits, but 3 blackcaps (Sylvia atricapilla) were not susceptible. Plasmodium vaughani of the robin, Erithacus rubecula, was transmitted to 1 robin and 1 blackcap, but 1 dunnock, Prunella modularis, was not susceptible. The prepatent period was between 8 and 10 days in all experimental infections. Maximum experimental parasitemia (3.4% of red cells) was detected in great tits infected with P. nucleophilum 23 days postexposure. A light (<0.01%) transient parasitemia of P. vaughani developed in the robin and blackcap. This study is in accord with former experimental observations on host specificity of P. nucleophilum and P. vaughani, which are characterized by a wide, but selective, range of avian hosts. Two new host-parasite associations were recorded.