Background/Objectives: Plasma zinc concentration is the preferred biomarker of zinc status, but the time of day and time since previous meals can modify the results. Measuring fasting plasma zinc concentration is not feasible among young children, so adjustments need to be developed for interpreting results. Our objective is to develop correction factors to adjust for the effects of time of day and interval since the previous meal when measuring plasma zinc concentrations of young children.Subjects/Methods: We measured plasma zinc concentrations among young Peruvian (n=297) and Ecuadorian (n=466) children, and constructed regression models adjusting for time of day, interval since previous meal and infections.Results: Plasma zinc concentrations were positively related to the number of hours since the previous meal in the Peru trial (r=0.22, P<0.0001) and negatively related to the time of day of blood sampling in both Peru (r0.24, P=0.0001) and Ecuador (r=-0.18, P<0.001). In multivariate models, plasma zinc concentrations were ∼2 μg per 100 ml less for each hour later in the morning when blood samples were collected, in both populations, and concentrations were ∼1.0 μg per 100 ml greater for every hour since previous meal consumption in Peru. The percentage of children with low plasma zinc concentrations varied according to both these factors.Conclusions: The time of day and the interval since the preceding meal should be recorded when measuring plasma zinc concentration and incorporated into the statistical analysis and interpretation when assessing population zinc status. © 2011 Macmillan Publishers Limited All rights reserved.