Polyvinylpyrroliclone (PVP) and poly(ethylene glycol) (PEG) solid dispersion systems with flavanone glycosides, naringin and hesperidin, and their aglycones, naringenin and hesperetin, were prepared, using solvent evaporation method, to enhance their dissolution rates that may affect their bioavailability. Drug release of both flavanone glycosides and their aglycones was directly affected by the physical state of solid dispersions. Powder-XRD technique in combination with scanning and transmission electron microscopy revealed that PVP polymer formed amorphous nanodispersion systems with flavanone aglycones, while such systems could not be formed with their glycosides, which are bulkier molecules. Fourier transform infrared spectra suggest the presence of hydrogen bonds between PVP carbonyl groups and hydroxyl groups of both flavanone aglycones. These interactions prevent the crystallization of naringenin and hesperetin aglycones in PVP matrix. On the other hand, the ability of PEG carrier to form hydrogen bonds with flavanone glycosides or aglycones was limited, and as a result both flavanone glycosides and their aglycones remain in the crystalline form. For this reason, the solubility enhancement of PEG solid dispersions was lower than when PVP was used as drug carrier. At pH 6.8, the % release of naringenin and hesperetin from PVP/naringenin-hesperetin (80/20 w/w) solid dispersion was 100% while in PEG solid dispersions, it was not higher than 60-70%. (c) 2006 Wiley Periodicals, Inc.