Abstract The construction of a quartz cell containing crystalline anthracene for continuous determination of carbon-14 and tritium in the effluent of the amino acid analyzer is described. The cell can be used with standard scintillation counters permitting efficiencies of 38% at 18 cpm background or 27% at 7 cpm background for carbon-14 and 0.9 and 0.7% with the same backgrounds for tritium. Depending on the choice of instrumentation the results can be indicated by a ratemeter and recorder, or they can be simultaneously printed on tape and indicated on the recorder of the amino acid analyzer. Carbon-14 and tritium can be determined in the same experiment in different amino acid peaks or, with the use of two channels in the conventional manner, in the smae peak. A carbon-14 activity of about 1000 dpm can be determined with a 5% standard error. Above 3000 dpm the error is 1–3%. About forty-fold higher activities are required for tritium.