The iodination of ethyl pyruvate in aqueous solution is kinetically of zero order with respect to iodine and is catalysed by bases: the observed rate is therefore the rate of ionization of the ester. The rate of ionization in the absence of catalysts other than water is approximately the same as that found previously for pyruvic acid, which weakens the evidence for intramolecular catalysis in the ionization of the latter substance. Basic catalysis by carboxylate anions in the iodination of ethyl pyruvate obeys the Bronsted relation, but the value of the exponent $\beta$ does not fall into line with values previously found for monoketones or $\beta$-diketones. No complex formation is detectable between iodine and ethyl pyruvate. The iodination reaction does not go to completion, and its equilibrium constant was measured. Values for the acid strength of ethyl pyruvate estimated from this equilibrium constant and from the rate of ionization are pK = 16.6 and pK = 15.4 respectively.