of plots relative to one another should take into account any environ- mental factors such as prevailing wind directions and field drainage patterns that would tend to confound (mix up) the clean-up treatment The use of two or more control plots in appropriate locaeffects. Also, an outline of the pertinent summary tables and probable results expected from the study would be useful at the planning stage, as would an outline of the statistical analyses to be tions is advisable. performed. Careful attention to detail at the planning stage should yield benefits over the long run. One feature of the study will be, apparently, to measure the degree of revegetation that occurs following the various clean-up treatments. The particular variables used to measure this effect must be selected with care to ensure that measurements obtained over time are truly comparable. Also, the variability in revegetation behavior from plot to plot that will be induced by the probable inability to apply a clean-up treatment with equal force to different plots suggests the need to have replicate plots for each treatment. Specifications of the optimum number of replicate plots per treatment will be difficult to ascertain due to lack of prior information. Slight differences in revegetation due to treatment effects are likely to go undetected. INTERLABORATORY COMPARISONS There is a need to continue the comparison of laboratories regarding their analytical results for plutonium or other radioisotopes. But there also needs to be a greater awareness of the limitations of such studies, relative to being able to detect differences between laboratories, when environmental samples are used. There are basically two types of samples that can be used for interlaboratory comparisons: "cross-check" and "standard" samples. Cross-check samples are environmental samples (soil, vegetation, etc.) collected either during the course of an ongoing field study, such as at an NAEG study site, or as special field samples collected with the express purpose of comparing laboratories' analyses. 111 Standard