The study has been designed to develop and evaluate the in vitro sustained-release capability of sorbitan monopalmitate (SMP) and castor oil (CO) based organogels. Organogels were prepared by heating the mixture of SMP-CO at 60 degrees C either with or without using distilled water (DW). The heated mixture was subsequently cooled to room-temperature to allow the formation of a gelled structure. Characterization of organogels was carried out by microscopy (light, fluorescent, electron, and atomic force), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), rheological study, pH, impedance spectroscopy, hemocompatibility, and antimicrobial studies. The properties and stability of the gels was dependent on the composition of the organogels. FTIR studies indicated the presence of strong intramolecular/intermolecular hydrogen bonding amongst the gel components. XRD studies suggested amorphous behavior of the gels. The gels showed a shear thinning behavior. Metronidazole (MZ) loaded gels showed good antimicrobial property to be used as an antimicrobial formulation. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1503-1515, 2013