Increasing knowledge of the neurochemical aspects of central nervous system function raises the possibility of treating Alzheimer's disease (AD) and other neurological diseases by the appropriate manipulation of neurotransmitters, neuromodulators, neurohormones or neurotrophic factors. Clinical application of this knowledge may, however, be inhibited by long standing problems with drug delivery to the central nervous system (CNS). Novel, CNS-directed, drug delivery systems might be used to overcome many of these problems. The problems encountered in drug delivery to the brain, present experience with the clinical use of some novel drug delivery systems and the advantages and disadvantages of these systems will be discussed.