[en] This report describes the results of an experiment conducted by Chemical Abstracts Service (CAS), on the use of 'data tags' in a machine-readable output file for incorporation into an on-line search service. 'Data tags' are codes which uniquely identify specific types of numerical data in the corresponding source documents referenced in the file. Editorial and processing procedures were established for the identification of data types; the recording, editing, verification, and correction of the data tags; and their compilation into a special version of ENERGY, a CAS computer-readable abstract text file. Possible data tagging plans are described and criteria for extended studies in data tagging and accessing are outlined