Conversion of crystalline alpha-, beta-, or gamma-cyclodextrins into amorphous mixtures of water soluble derivatives yields non-toxic solubilizers which dissolve drugs through the formation of inclusion complexes. From these types of compounds 2-hydroxypropyl ethers of cyclodextrins have presently been investigated and the ranges for the safe use in working with (a) receptor binding assays on membrane preparations, (b) cells in vitro, and (c) parenteral use in mice were established for these compounds. The drugs which were investigated were dissolved in amounts linearly proportionate to the concentration of the solubilizers used and did not precipitate upon dilution by aqueous media. These solubilizers may considerably facilitate pharmacological evaluation of new, water insoluble potential drugs.