A rapid oxidizing combustion method using a commercial Sample Oxidizer has been investigated to determine separately the C-14 and H-3 activities in graphite and concrete. By this method the sample preparation time can be reduced to 2-3min. The detection limits for H-3 and C-14 are 0.96 and 0.58Bq/g graphite and 0.11 and 0.06Bq/g concrete, respectively. The cross contamination of C-14 and tritium in the preparation of samples is less than 0.2%. The interference of other radionuclides in the determination of C-14 and tritium in graphite is insignificant. The analytical accuracy, investigated by the standard addition method, is better than 95%. In addition, an acid digestion method has also been used to examine the graphite and concrete activities, to allow comparison with the method developed herein. The two methods show good agreement for graphite samples. Graphite samples were collected from the Danish Reactors DR-2 and DR-3, in addition to two concrete cores drilled in the Danish reactor DR-2; these were analysed for H-3 and C-14 using the method that has been developed. (c) 2005 Elsevier Ltd. All rights reserved.