The acetylene reduction assay is an indirect measure of biological nitrogen fixation used extensively to screen species for nitrogenase activity, as well as to determine environmental controls on and to estimate annual rates of nitrogen fixation. The assay is a simple, inexpensive, and sensitive measure of nitrogen fixation; however, the ability quantitatively to estimate nitrogen fixation decreases when assays are conducted at remote field sites (Waughman 1971, Stutz and Bliss 1973). Decreased precision and accuracy result, in part, from the need to transfer and store gas samples, as well as differences in temperature and pressure among containers, field sites, and laboratory. Thus, development of quantitative gas handling techniques is essential to conducting field tests. We solved the problem of quantitative gas transfer while studying nitrogen fixation by Ceanothus velutinus var. velutinus and Shepherd/a canadensis in the Blue Mountains of northeastern Oregon. Special conditions we faced were: the field sites were 500 km from the laboratory; often several weeks would elapse between field sampling and gas analysis; and only a small portion of the gas could be retained for analysis. The use of acetylene (C2H2) as an internal standard was the solution to gas transfer problems at remote field sites. An internal standard is a pure compound of known concentration added to a sample to establish a proportional relationship between its concentration and that of an unknown. In this case, the unknown was the ethylene (C.,H4), produced during nitrogen fixation (Grob 1977). As a basic analytical technique that can correct for instrument variation (Kaiser and Debbrecht 1977), an internal standard eliminates the need to measure sample volume during quantitative analysis. Acetylene is an ideal internal standard because it is inherent to the acetylene reduction assay and is analyzed simultaneously with ethylene from a single gas injection (Hardy et al. 1968). The only requirements are premeasurement of the C.,H2 concentration injected into reaction vessels and preparation of standard curves for C.,H2 and C2H4. The use of C.,H., in reduction assays has been ignored in favor of direct volumetric transfer of gas samples. However, gas analysis by gas chromatography (GC) generally is not regarded as quantitative because of problems with sample injection (Littlewood 1970). Thus, using syringes to transfer gas samples volumetrically from reaction vessels to a GC column is an imperfect analytical technique. The technique we describe eliminates volumetric transfer of gas samples from field sites to the laboratory and from vials to the GC column.