Background: Human embryonic stem cells (hESCs) and in-duced pluripotent stem cells have great potential for model-ling and treating neurodegenerative diseases as they are able to differentiate into neuronal and glial cell linages in response to appropriate signals. Parkinson’s disease (PD) is one of the most common neurodegenerative disorders affecting older people and is characterized by degeneration of dopaminergic neurons in the substantia nigra, leading to tremor, muscle rigid-ity and instability in movement. The ineffectiveness of current medications for PD has motivated the development of thera-pies based on hESC-derived ventral midbrain (VM) progenitors which have the potential to replace the neurons lost due to the disease, thereby restoring the dopamine levels in the patient s brain. A current challenge, however, is to track the transplanted VM progenitors and determine their contribution to functional recovery. Therefore, the first aim of this study was to implement a non-invasive imaging strategy that would allow the behav-iour of hESC-derived VM progenitors to be monitored non-in-vasively following stereotactic injection into the rat brain. The second aim was to determine if the labelling techniques used to visualise the cells in vivo had any effect on the tumourigenicity, differentiation potential or immunogenicity of the injected VM progenitors.Materials and Methods: To visualise the cells, we used a bi-modal imaging approach that allows the viability and tumouri-genic potential of luciferase-expressing hESC-derived VM cells to be monitored with bioluminescence imaging (BLI), and the intracranial biodistribution of VM progenitors labelled with fluorescent iron oxide particles (IOPs) to be assessed with mag-netic resonance imaging (MRI). To assess the differentiation potential and immunogenicity of the VM progenitors, at the end of the experiment, histological sections were analysed to assess the effect of the labelling strategies on VM differentiation (ty-rosine hydroxylase expression), and immunogenicity (staining for GFAP, a marker of activated astrocytes).Results: The preliminarily results showed that the engrafted-VM progenitors formed neurons that expressed the dopamin-ergic neuron-specific marker, tyrosine hydroxylase (TH), sug-gesting that the labelling techniques did not negatively impact on the ability of the VM progenitors to mature and differenti-ate into TH+ neurons in vivo. Moreover, BLI and MRI showed no evidence for tumour formation post implantation, suggest-ing that the progenitors are not tumourigenic, irrespective of whether they express a genetic reporter, or are labelled with IOPs. MRI showed that the cells remained within the striatum and did not migrate to other brain regions.Conclusion: Histological analysis showed that the labelling techniques did not affect the ability of the VM progenitors to differentiate. However, we observed that the presence of IOPs, but not luciferase, increased the extent by which GFAP+ host astrocytes accumulated around the hESC-derived cells.