An automated method for the simultaneous analysis of total N, total C,15N and14C in small plant and soil samples is described. A commercial C‐N analyser ‐ continuous flow isotope ratio mass spectrometer (ANCA‐MS) has been extended to also measure CO2and collect14CO2produced by sample combustion. Samples containing 20 ‐ 200 μg N and up to 5 mg C can be analysed directly with no sample preparation other than drying and fine grinding. The precision of total elemental analysis is comparable to that by conventional methods. The average standard deviation of15N analyses of plant material at natural abundance was ±1 ‰. This is accurate enough for all15N studies except those using natural abundance and possibly long term studies of soil organic matter. Recovery of14C in test samples was 100%. The instrument can be operated by graduate students under supervision and operating costs are primarily for sample cups, combustion catalyst and quartz tubes.