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We have attempted to determine the appropriate temperature for sample storage and the stability of five proteins in serum for up to two weeks: immuno-globulins G, A, M, complement C3, and complement C4. Whole blood was sampled from vol-unteers, allowed to clot, promptly cen-trifuged, and the serum was separated. The proteins were then assayed imme-diately, in triplicate and within the same assay run to eliminate any run-to-run variability. The remaining serum from each specimen was divided into nine portions, three of which were stored at each of three different temperatures:-6 #{176}C,4 #{176}C,and 22 #{176}C.One, seven,and 14 days later, we assayed aliquots of the sera from each storage condition, again in triplicate. The frozen aliquots were used only once and discarded (no thawing and refreezing). We used the Model 290 Light Scat-tering Nephelometer and reagent kits (Kallestad Laboratories, Chaska, MN 55318) to measure the proteins men-tioned above. Our results are summa-rized in the following tabulation