Experiments are described on the dehydrogenation of butene-1 in the presence of steam, over three nickel chromite catalysts. These are: (a) pure nickel chromite, (b) nickel chromite pellets impregnated with potash from solution, and (c) a catalyst with potash added before the nickel oxide and chromium sesquioxide are combined. The oxidation state of the catalyst largely affects the products, for overreduction causes disruption of the hydrocarbons. The effect of the potash is to prevent this overreduction and thus to improve selectivity to butadiene. There is a difference between the behavior of catalysts with surface potash (type b) and those where the potash is distributed through the mass (type c). This difference is explained by the formation of large pores on reduction of type (c) catalysts.