Study on concurrent Trypanosoma cOllgo/ellse and Haemonchus COllrortliS infections to assessrnthe interaction and pathogenic effect of single and mixed experimentally induced infection werernconducted in goals. A total of 25 goats of approximately one year old were divided into fiverngroups and each group was infected either with H. COlltorWs one week after a preceding infectionrnwith T. congo/elise or with primary H. conlOrlus infection one week prior to T. cOllgo/ellse orrninfection with either the nematode or trypanosome alone, and the fifth group was served as nonrninfected control. For experimental purpose each experimental animals were infected with T.rncongo/elise. derived from the donor goat after one passage in mice with total intravenousrninoculation of 5x I 4 T. congo/elIse. The tOlal infective dose of H. cOl/torll/S, which was givenrnorally to each animals was, 10,000 3rd stage larvae. Parasitological observations such as prepatentrnperiod, faecal egg count, woml burden and trypanosome parasitaemia; and hematologicalrnparameters like packed cell volume, haemoglobin concentration. mean corpuscular volumern(MCV), mean corpuscular haemoglobin concentration (MCHC), red blood cell counts, whiternblood cell coul1ls. differential leukocyte counts (eosinophil, lymphocyte and neutrophils), totalrnprotein and also clinical parameters including body weight change, mortality rates among variousrntreatment groups were made in mixed infected groups and in animals singly infected with ei therrnparasites. It was revealed that the order of infection in the preceding or subsequent infection wasrnvery important in which the most hannful combination was a primary T. cOllgo/eflse infectionrnone week prior to Ii. COllforllls super Infection. that resulted in progressive and sever anaemiarnaccompanied by leucopenia, hypoprOleinemia, loss of weight and short prepatem period of H.rnCOlftorlllS. Except animals mono infected with H. COnforms, which have shown macrocyticrnhypochromic anaemia, all other treatmem groups have revealed nomlocytic nonnochromicrnanaemia throughout the whole observation period. The result also showed that animals withrnconcurrent T. cOllgo/ellse and Ii. COI/lortus run high risk of succumbing during the infectionrnperiod. Higher rate of mortality and more pronounced pathological effects were observed inrncombined infections than single ones. It was concluded that the increased I/. cOlllortus eggrnexcretion observed in animals infected with both parasites might signi fi cantly increase the risk ofrnnematode infections. The interaction between these two highly potent anaemia causing pathogensrnshould be considered whenever attempts are made to control these two diseases.