1. Decide on what organ or other biological material to study and select the proper compound for this study from the knowledge of precursor acid metabolism. Develop the RIA for this compound or a stable derivative thereof. 2. Whichever sample type is assayed (extracted or unextracted), the possibility of the presence of nonspecific interfering factors must be constantly kept in mind. Make dilution tests and assay for parallelism; however, do not accept parallelism as an absolute criterion of absence of nonspecific influence. 3. Use two or more completely different separation techniques for comparison when validating the RIA. 4. When evaluating the RIA, do not limit the investigation to the traditional reliability criteria: sensitivity, specificity, precision, and accuracy. The RIA may seem reliable at this stage and still give completely unrealistic values when applied to biological material. The method must be evaluated by other studies as well. 5. In the experimental design, aim at following the changes in prostaglandin levels in a series of samples instead of measuring absolute levels in single samples. 6. Make comparative studies employing different quantitative methods.