The Gas Metrology Research Group of the National Institute of Standards and Technology (NIST), has been involved in research and development of gas standards of volatile toxic organic compounds for many years. Over thirty toxic organic compounds have been studied in gas mixtures contained in high pressure aluminum gas cylinders with specially treated interior surfaces. Almost all compounds studied to date have shown very good long term stability at the parts-per-billion (ppb, nanomole/mole) to parts-per-million (ppm, micromole/mole) range. One exception, 1,3-butadiene, is a compound that many scientists and policy makers are very interested in measuring in the environment. The author discusses data obtained over several years for gas mixtures of 1,3-butadiene in nitrogen, at concentrations of 2 ppm, 100 ppb, and 10 ppb. The data demonstrate that mixtures of 1,3-butadiene at the 2 ppm level have remained stable for over three years. However, gas mixtures of 1,3-butadiene at the 10 ppb level have shown decreases in concentration of more than 70% over a two-year period. Decreases in the concentration of 1,3-butadiene have been observed immediately after the preparation of the gas mixture in several cylinders. This indicates that gas mixtures of 1,3-butadiene are not stable at the ppb levels and therefore are not reliable as accurate calibration standards.