The feasibility of using a simple radiochemical method to determine the extent of formylation resulting from interaction of formic acid solutions with soil constituents was investigated. The interaction between formic acid‐l4C solvents and starch was used as a model reaction. Radioassay of 1 cm3formic acid solution by liquid scintillation counting in 10 cm3of the scintillator‐solubilizer Insta‐gel was found to be suitable. The method is simple to use and sample preparation is easy.