Hydroxypropyl cyclodextrins, chemical derivatives of glucose oligosaccharides, which were originated in the section, form water soluble complexes with lipophiles. Since these derivatives are also non-toxic they have been used as drug solubilizers with enough of success to qualify them for consideration to be included in the next edition of US Pharmacopea/National Formulary. The present chemical results point out the structural elements which are critical for the acceptable performance of hydroxypropyl cyclodextrins in biomedical applications. The present biological results point to a possible health hazards which may result from the ingestion of very large doses of hydroxypropyl cyclodextrins.