The kinetics of the dehydration of methylene glycol were measured under conditions relevant in industrial formaldehyde absorbers (293 K less than or equal to T less than or equal to 333 K; 6.0 less than or equal to pH less than or equal to 7.8). The rapid reaction between formaldehyde and SO32- to hydroxymethane sulphonate (HMS-) was used as a formaldehyde scavenger: [GRAPHICS] [GRAPHICS] [GRAPHICS] Under the experimental conditions the rate determining step in the formation of HMS- appeared to be the dehydration of methylene glycol. The observed reaction rate constant for the dehydration of methylene glycol could be correlated as k(d) = 4.96 x 10(7) x e(-6705/T) s(-1). The dehydration rate is shown to be independent of the concentrations of both sulphite and hydroxide ions.