The development and application of two methods for the determination of sterilization residues in ethylene oxide sterilized steroids, vitamins, and antibiotics are described. One method is based on the separation and concentration of ethylene oxide (ETO) by distillation and measurement by internal standard gas liquid chromatography. The other method, based ultimately on the colorimetric determination of formaldehyde, permits determination of total glycol as well as specific ETO and glycol after ion exchange or extraction separation procedures. The mechanism of retention is discussed, with particular emphasis on solvation phenomena.