Placental hGH-V and pituitary hGH-N are of identical size (22kDa) but differ in 13 residues scattered throughout the protein. Several isoforms of GH are produced by the hGH-N and hGH-V genes including a 20kDa hGH-V resulting from a 45bp deletion caused by the use of an alternative acceptor site within exon 3. To date, the biological properties of the 20kDa GH-V have not been characterised in-vivo. Using young male Wistar rats fed either chow or a high fat (HF) diet for 4 weeks post-weaning, we investigated the effect of 7 days treatment with either 22kDa hGH-N, 20kDa hGH-V (5ug/g/day, sc) or vehicle on body composition and endocrine and metabolic profiles. Total body growth (absolute weight gain and linear growth trajectory) in the 20kDa hGH-V treated animals was intermediary between that of control and hGH-N treated animals. Both 22kDa hGH-N and the 20kDa hGH-V significantly reduced total body fat mass compared to control animals and there were no differences between the GH isoforms in anti-lipogenic activity in animals fed the HF diet. Fasting plasma insulin and C-peptide were significantly increased in animals on the HF diet and further increased by hGH-N but were unchanged in 20kDa hGH-V treated animals compared to saline treated controls. Plasma volume as assessed by hematocrit was increased in hGH-N treated animals but was unchanged in 20kDa hGH-V treated animals compared to controls. Furthermore, the 20kDa hGH-V had reduced lactogenic (prolactin receptor mediated) activity characteristic of hGH-N as tested in vitro compared to the 20kDa hGH-N and 22kDa hGH-N variants. In summary, placental 20kDa hGH-V retains some of the growth promoting and all anti-lipogenic activities of pituitary 22kDa hGH-N but has diminished diabetogenic and lactogenic properties compared to the native 22kDa hGH-N.