An alternative method to the use of the disposable Kontes well for trapping 14CO2 produced in the course of biological oxidations is described. 2. A polyethylene miniature scintillation vial was used to contain the hyamine hydroxide-impregnated filter paper wick. 3. The two methods are compared in their abilities to trap 14CO2 produced directly by acidification of sodium [14C]bicarbonate and during beta-oxidation of 1[14C] palmitic acid. 4. The miniature vial and Kontes well methods showed similar efficiencies in the trapping of 14CO2 (97% and 95%, respectively, on average) the radioactivity of which was determined in the miniature vial using 5 ml only of scintillation fluid compared with a minimum of 10 ml required by the standard scintillation vial used to accommodate the Kontes well. 5. The technical advantages of the suggested miniature vial system, during both incubation and counting stages, are discussed.