The main problem associated with Neospora caninum and the corresponding disease, neosporosis, are abortions in cattle causing serious veterinary health issues and economic losses within livestock production. In the work presented here, the efficacy of toltrazuril, an anti-coccidial drug, was further investigated using two approaches: (I) a mouse model to assess the effect of the drug on congenitally acquired N. caninum-infection in newborn mice and (II) cell culture-based assays to assess treatment duration time for parasitostatic versus parasiticidal activity. Furthermore, the work was directed to establish a novel molecular detection method to clearly distinguish between live and dead parasites. The last part of the thesis work concentrated on the immune response induced by N. caninum. To pursue this, interaction of N. caninum with dendritic cells (DCs) was examined, as nothing is known so far about the invasion ability of N. caninum into DCs and the survival of parasites in these cells.