The present proposal concerns a PEGylated, hydrophobic drug containing polylysine dendrimer that demonstrates unexplained batch-to-batch variability in that two batches of the AZD0466 drug-dendrimer conjugate exhibit slightly different particle sizes and in vivo behaviour, whereas drug loading and drug release is similar for both batches. SANS in combination with contrast variation will be used to determine how the molecular architecture of the dendrimer molecules alters in the presence of drug and by changing solvent (from water to methanol). The information obtained in the present study will be invaluable in understanding how these dendrimer nanoparticles can be successfully exploited as drug delivery vehicles.