Phospholipid synthesis, interconversion and breakdown in T. rubrum were followed by radioactive tracer. Synthesis and catabolism of phosphatidyl ethanolamine and phosphatidyl serine are most rapid; phosphatidyl choline and phosphatidyl inositol are metabolised rather slowly. Catabolism of phosphatidyl ethanolamine and phosphatidyl serine are uniform and their conversions to phosphatidyl choline and phosphatidyl inositol are suspected. © 1977 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.