In birds, concentrations of testosterone (T) and corticosterone (Cort) are closely connected with many morphological, behavioural and other physiological traits, including reproduction, metabolism, immunity, and fitness. The direction of the effect of these hormones on above-mentioned traits, and the potential feedback between hormones are in general unclear; in addition, knowledge on how age and sex can affect T and Cort concentrations is still inconsistent. Our study used a novel method to analyse testosterone and corticosterone in feathers (Tf, Cortf) based on the pre-column chemical derivatization of hormones before LC-MS/MS analysis. Unlike previously used methods (RIA, EIA), our analytical procedure allows simultaneous analysis of both hormones from small amounts of feathers (4-25 mg) and thus overcomes the problem of insufficient detection limits. We applied this method to reveal associations between Tf and Cortf hormone concentrations and feather growth, age, and sex in feathers grown during the post-breeding (flanks) and pre-breeding (tails) periods in barn swallows (Hirundo rustica). There was neither a correlation between pre-breeding and post-breeding Tf, nor between pre-breeding and post-breeding Cortf. Tail Cortf concentrations were negatively associated with tail feather growth rates. Feather hormone concentrations were correlated in the pre-breeding period, negatively in males but positively in females. Both Cortf and Tf were higher in young birds compared to older ones, indicating either an age-related decrease in hormone concentrations within individuals, or the selective disappearance of individuals with high steroid concentrations. Males and females did not differ in Cortf, but Tf concentrations were higher in males than females, particularly during the pre-breeding period. In this study, we provide an effective method for analysing hormones in feathers in an ecological context, especially in situations when the total amount of feathers available for the analysis is limited.