Recently metaldehyde toxicity was reviewed. The review article made two references to analytical methodology of which one gave a personal communication as a method and the other was for a simple colorimetric test which suffered the disadvantage of being only semi-quantitative. Since the review a detailed gas-chromatographic technique specific for metaldehyde has been reported for plasma and urine. We now report on an extremely sensitive and rapid determination of general volatile carbonyl compounds, including acetaldehyde liberated from metaldehyde, as their 2,4-dinitrophenylhydrazone adducts whilst overcoming all of the difficulties and cumbersome manipulation previously needed with these adducts. The test has the advantage of being colorimetric and furthermore gas chromatography can be utilized to quantitate the acetaldehyde liberated by acid hydrolysis of metaldehyde and to separate it from the adducts formed by formaldehyde, acetone and similar compounds. Acetaldehyde and its polymers can be separately analyzed, when desired, by a simple additional step.