1.1. Dynamics of plasma nutrients and metabolites in moulting macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins were studied.2.2. The late moult macaroni and gentoo penguins had significantly elevated levels of total lipid and cholesterol, α-tocopherol (vitamin E) and alkaline phosphatase activity compared to early moult birds.3.3. Conversely, the mean concentrations of total protein, albumin, globulin, urate, creatinine, iron, calcium, inorganic phosphate, all-trans retinol and the activity of aspartate transaminase were lower in the late moult groups in both species.4.4. Mean concentrations of lipid, cholesterol, retinol (vitamin A), α-tocopherol (vitamin E), total protein, albumin, globulin, calcium and sodium were higher in the pre-moult than in the early moult macaronis.5.5. Dietary influence may partly account for the higher nutrient status of the pre-moult birds.6.6. Both the early and late moult macaronis had raised levels of total lipid, cholesterol, a-tocopherol and potassium compared to the corresponding gentoos.7.7. Total protein, albumin, globulin, sodium and inorganic phosphate concentrations, however, were higher in the later species.8.8. Differences in the levels of the plasma nutrients between the early and late moult macaronis, and their counterpart gentoos is due to species-specific variability.