A drug delivery system with cubic liquid-crystalline phase structure (cubic phase) containing the anti-cancer drug Carboplatin is studied. It is demonstrated that the combination of pulsed field gradient (PFG) NMR and MAS-NMR is a useful tool to study the biophysical properties of a cubic phase. The linewidth in H-1-NMR spectra is narrowed by MAS, which can be exploited to perform PFG diffusion NMR experiments under high-resolution conditions. Measurement of self-diffusion coefficients of all components of the cubic phase becomes possible, The influence of polyethylene glycol chains on the drug mobility is discussed. It is shown that polyethylene glycol chains interact with Carboplatin. (C) 2002 Published by Elsevier Science B.V.