ABSTRACT Body condition is an important ecological attribute that can provide a measure of the energy stored by an animal or population. Body condition is traditionally ascertained with morphometric body condition indices (BCIs), but some researchers have used various physiological and biochemical parameters as predictors of body condition. This study aimed to test reliable biochemical predictors of body condition in individuals of Neopelma pallescens (Lafresnaye, 1853), found in an Atlantic forest patch. For this purpose we examined the relationship between body condition and the concentrations of blood glucose and ketones. We also verified correlations between blood metabolite concentrations and ecological variables, including time of day, seasons, breeding periods, and ectoparasite infestation. Birds were captured with mist nets at Reserva Biológica de Guaribas, state of Paraíba, Brazil. Blood samples were analyzed with a portable glucometer. The correlation between glucose and ketones was negative. Both metabolites showed significant variations according to time of day. Glucose levels were higher in the afternoon and ketones levels were higher in the morning, suggesting a correlation with daily food intake. The BCI of non-breeding birds was negatively correlated with glucose concentrations. However, the correlation between glucose and the BCI of incubating birds was a positive. Ketone bodies did not correlate with body condition. In relation to ectoparasite infestation, only ketones showed significant results, presenting a higher concentration in infested individuals. Glucose is a good predictor of the BCI of incubating birds since it correlates positively with it. However, the lack of seasonal variations in metabolites indicates that the nutritional status of tropical birds does not change when food is abundant. Thus, we conclude that glucose and ketone bodies can predict the nutritional status of birds but in a context-dependent fashion.