AbstractRadiochlorine38 was evaluated and found to be suitable for use as a tracer in studying the deposition of fat in porcinepanniculus adiposus tissue. Its short half‐life makes its preparation from natural chlorine simple and inexpensive, and also minimizes long‐term contamination problems, and its energetic beta and gamma rays makes its radio‐assay simple and rapid. For swine, the threshhold level for a statistical counting accuracy of 1% was found to be approx 8 ȕ 10蜢2 mc/lb of live wt. The time required for the digestion, absorption, transport and deposition of statistically sufficient detectable radioactive material was 3 1/2 hr. The incorporation of radiochlorine38 into lipid molecules does not appear to alter their normal metabolic pathways.