Cultures ofGomphosphaeria aponinawere subjected to continuous cell centrifugation and the cell‐free medium was re‐used. The growth constants for the organism, Ke, the maximum cell number, the yield of cytolytic agent (at ten days) all increased using recycled medium. Growth constants based upon chlorophylla(in vivo) content did not increase. Iron concentrations at the outset of both culture series (fresh and recycled medium) were the same, but the recycled medium interfered in the analysis of iron using a colorimetric procedure and a Technicon AutoAnalyzer II. Negative values of iron concentration were obtained, and dissolved iron had to be added to obtain base‐line values. It was possible to quantitate the iron‐complexing capacity of the solution, though the materials responsible for the interference are unknown.