Magnetic data tapes have been aged at several temperature and relative humidities. Data previously recorded on the tapes was read back after aging and the inability to read such data was used to make a preliminary estimate of tape lifetime. Based on this criterion we estimate a useful tape lifetime of 20 years at ambient conditions. This involves a long extrapolation, however, because there have been few failures at humidities lower than 100per thousand and temperature below 85°C, and only one failure at all below 60°C. The tape lifetime estimate should be considerably more certain by the time of the final report in this series which will be issued in November 1987. There are documented reports of tape failure after ten years of storage under normal room temperature and humidity and we have seen cases of failure after only a few years so lifetimes can vary considerably. Reading failures wit rapidly-aged tapes appear to be caused primarily by exudation of material from the binder layer. This accumulation on the reading heads or makes the tape stick to the tape transport. In order to test the condition of tapes before failure, three tests were devised that measure adhesion or extensibility of the binder layer. Water content and weight changes on aging were also measured. None of these five secondary quantities correlated quantitatively with the ability of a tape transport to read data previously written on the tapes, but some of them are useful indicators of risk.