PURPOSE: To enable the enzymic determination of carbon dioxide in a body fluid containing a carbonic anhydrase by taking a step for bringing acetazolamide into contact with the body fluid and a step for measuring a change in concentration of a specific compound in the resultant mixture.

CONSTITUTION: A step for using a multilayer dry element, containing a spreading layer, containing acetazoleamide and capable of manifesting pH 7.0-9.0 when wetted, a reagent layer comprising a phosphoenolpyruvate carboxylase, phosphoenolpyruvate and a recording layer comprising reduced nicotinamide adenine dinucleotide and maleate dehydrogenase and prepared by a laminating method or a coating method and mixing a prescribed amount of a body fluid such as human blood with an excessive amount of the reagent is passed to maintain the resultant mixture at a prescribed temperature and a prescribed pH. A change in the reduced nicotinamide adenine dinucleotide concentration in the mixture produced thereby is measured by a spectrophotometer.