2-Hydroxypropyl-beta-Cyclodextrin are non-toxic solubilizers. The solubility of drugs increases linearly with the concentration of 2-Hydroxypropyl-b-cyclodextrin in aqueous buffer. The formation of drug/cyclodextrin complexes is a rapidly reversible reaction and complexes exist both in solution and crystalline states. Solutions of many such complexes may be lyophilized to produce freely soluble powders which may be compressed into tablets. Bio-effects are only slightly affected by cyclodextrin complexation. Cells in serum supplemented medium can be grown in up to 1-2%. In serum-free medium, concentrations of 0.5-1% are acceptable. Hydroxypropyl-b-cyclodextrin has been found to be non-toxic in mice and rabbits. 2-hydroxypropyl-g-cyclodextrin with its 8 glucose units, has a slightly larger cavity and can accomodate larger substrates than the beta form. The use of cyclodextrins in receptor binding assays in not recommended.