Prostaglandin (PG) F2 is synthesized via three pathways from PGE2, PGD2, or PGH2 by PGE 9-ketoreductase, PGD 11-ketoreductase, or PGH 9-, 11-endoperoxide reductase, respectively. The enzymological and molecular biological properties of these enzymes have been reported in work over the last 30 years. Here, these three pathways of PGF synthesis by these enzymes are reviewed, and the physiological roles of the enzymes are discussed.