Complete and rapid removal of ethylene oxide used for fumigation and its conversion products are of critical importance when reusing gas-sterilized parts of instruments. Evaluation of desorption is possible by means of gaschromatographic analyses of the atmosphere in packs containing the instruments for fumigation and storage. Residual amounts for a number of selected parts of instruments shown suggest latent sources of danger. The dimension of the instruments, the differences in plastic materials and ethylene oxide permeability of packing materials play a significant, though not obvious, role. Since no general rules concerning the duration of desorption can be established in view of these various factors, occasional examinations by means of gaschromatographic analyses are necessary.