In the present investigation, the pathogenicity and transmission of a mono-eukaryotic culture of Histomonas meleagridis for commercial turkeys and specific pathogen free (SPF) chickens is described for the first time. Two separate trials with the same kind of experimental design were performed, one with commercial turkeys and one with SPF chickens. In each experiment, two different groups were included, which were housed in separate rooms. The first group contained four control birds, whereas the second group consisted of 10 infected and four in-contact birds. The birds were infected via the cloaca at 14 days of age with 380,000 cells of a mono-eukaryotic culture of H. meleagridis consisting of a cloned isolate (Turkey/Austria/2922-66/04). Reisolation of the parasite from turkeys and chickens under experimental conditions was performed for the first time. The infected birds started to excrete the parasite as soon as 2 days post infection. Rapid spread of the parasite to in-contact turkeys and chickens was noticed, based on reisolation of live parasites. Reisolation of the pathogen was impossible from two of the four in-contact SPF chickens at any time, whereas all of the infected turkeys were found positive. Intermittent shedding of the parasite was noticed in infected turkeys and SPF chickens, but the phenomenon was much more severe in the SPF chickens as these birds survived the infection. All of the infected and in-contact turkeys died between days 11 and 14 post infection, whereas no death was recorded in the SPF chickens, which were killed 6 weeks after the infection. Typical lesions were recorded in the caeca and livers of the infected turkeys. In addition, a heavy destruction of the bursa of Fabricius was seen in all of the infected and one of the in-contact turkeys. Altogether, the present investigations are of importance for an understanding of the pathogenicity and transmission of H. meleagridis in poultry.