The stability of polybutylcyanoacrylate (PBCA) nanoparticle suspensions was examined by measuring particle sizes and size distributions over a period of 2 months in different solutions (hydrochloric acid, phosphate buffered saline). When stored in acidic medium, nanoparticles were found to be stable for at least 2 months. In this case, degradation of the polymer is decelerated and particle agglomeration is reduced. When added to human blood serum, nanoparticles were found not to agglomerate, remaining stable in size for at least five days. Previous stabilization protocols required lyophilization and resuspension by ultrasonification; however, the technique presented here using acidic storage solutions proves to be superior for clinical applications.