Buckwalter and Dickison1recently reported a new repository type of penicillin product.2They introduced the principle of suspending penicillin salts in peanut oil gelled with aluminum stearates, water repellent substances. They compared the absorption-delaying properties of this vehicle with the conventional repository vehicles in animals. The study recorded here was designed to carry this comparison further—in human subjects. The facilities of four assay laboratories were used, and assays were performed by two different methods, a modified Rammelkamp method and a cup plate procedure employing Sarcina lutea. Control samples of blood were drawn before the injection; each patient then received 300,000 units of penicillin in repository form, and consecutive samples of blood were taken at the intervals indicated on the chart. The lines on the chart are the lines fitted by the method of least squares to the logarithm of the average blood concentration with time in hours. Table