The removal of methyl iodide from containment atmospheres by reactive sprays proceeds by a simultaneous process of absorption and chemical reaction. A theoretical development is presented to show how the relative values of reaction time and other time constants of the system determine the rate-controlling process. Theoretical predictions are compared with the results of 12 experiment So For the fast-reaction case (when the reaction time is equal to or less than the fall time of the drops), the calculated removal half-times averaged 2.25 times the observed. The reasons for the difference are identified and appear to be due to erroneous equilibrium data, neglect of internal circulation in the calculation, and neglect of wall effects. A reduction factor of at least 2.0 in the 2-h dose due to methyl iodide appears readily attainable.