The material was prepared from black tea, usually packed in tea bags. Tea leaves collected and processed in Argentina were ground and sieved. All precautions were taken to avoid contamination of the material with metals. The next step was homogenization by mixing in a plastic drum. After preliminary homogeneity checking by X-ray fluorescence, the material was distributed into PP bottles and final homogeneity testing was performed by neutron activation analysis determining Br, Ce, Co, Cr, Cs, Fe, K, La, Mn, Na, Rb, Sc and Sm in subsamples (Fisher’s test). Good homogeneity of INCT-TL-1 at least for sample weight of 5 mg was confirmed. Long-term stability has been assured by sterilization of the whole lot of the material by electron beam radiation and is being monitored during storage. Certification of the candidate reference material was done on the basis of world-wide interlaboratory comparison exercise in which 109 laboratories from 19 countries using various analytical methods, participated. Data evaluation was performed using the software package ACQS-1. Several criteria were employed to decide whether the overall mean can be given the status of recommended (certified) or information value. The validity of certified values was confirmed for several elements using definitive methods developed in this Laboratory.