The surface of the cell is rich in carbohydrate moieties attached to b
oth membrane glycolipids and glycoproteins. These oligosaccharides con
stitute potential recognition sites for carbohydrate-mediated interact
ions between cells and drug carriers bearing suitable site-directing m
olecules. Liposomes constitute a potentially valuable type of drug car
rier. The ability to incorporate various site-binding molecules into t
he liposomal surface leads to a wide range of delivery systems based o
n carbohydrate-mediated interactions. In this review the types of reco
gnition site on the surface of mammalian cells are considered with reg
ard to both their chemical composition and the physical constraints wh
ich might effect their recognition by drug carriers with site-directin
g groups. Of particular current interest are the cell surface carbohyd
rate-binding proteins (lectins) which have yet to be fully exploited a
s recognition sites for carrier systems. Potential liposomal drug carr
iers have been considered under a range of headings: glycolipid-bearin
g, glycoprotein-bearing, virus spike glycoprotein-bearing (the so-call
ed 'virosomes'), antibody-bearing immunoliposomes, lipopolysaccharide,
polysaccharide-bearing and lectin-bearing. Examples of the applicatio
ns of these various types of liposomes and their targeting to recognit
ion sites on cells are reviewed. It is clear that while these systems
could be of considerable value for the targeting of drugs, a great dea
l more work has been reported on the preparation, control and targetin
g of liposomal systems involving carbohydrate-mediated interactions th
an has been reported on their actual use for the delivery of specific
drugs to cells. Carbohydrate-mediated drug delivery using liposomes is
a very sophisticated approach which will not be easy to exploit witho
ut very considerable investment. At present, much of the technology re
quired to exploit carbohydrate-mediated interactions in drug delivery
is available and future progress will depend on a determination to use
this technology to develop drug-carrying liposomal systems. The diver
sity of potential systems is large and the choice of liposomal system
for targeting a drug to a particular cell type will have to be determi
ned by balancing specificity of the liposomal carrier against ease of
production.