This file contains data for an experimental inoculation project aimed at understanding physiological impacts of Plasmodium in breeding-condition songbirds. The 'readme' tab contains explanations for columns on each spreadsheet. We first compared metrics of health (mass, scaled mass, hematocrit, activity rate) and reproductive readiness (cloacal protuberance volume, maximum testosterone concentration in plasma) in male songbirds (Dark-eyed junco, Junco hyemalis hyemalis) with and without chronic Plamodium infections. Then, we quantified the change in these metrics following experimental inoculation with Plasmodium, and asked whether these changes varied between males with and without chronic Plasmodium infections.