The cyclic undecapeptide cyclosporin A (CyA) a potent immunosuppressive drug used in many therapies, is extremely hydrophobic. Commercial products employ solubilising agents to improve gastrointestinal absorption. In the present study CyA solid lipid nanoparticles (SLN) are prepared from warm o/w microemulsion, dispersed in cold water. The matrix chiefly consists of stearic acid, phosphatidylcholine and taurocholate; up to 13% of CyA can be incorporated. The average diameter of CyA-loaded SLNs is below 300 nm and transmission electron microscopy (TEM) analysis shows them to be spherical. In vitro release of CyA from SLNs is low. CyA-loaded SLNs can be proposed for most administration routes, in particular for the duodenal route.