We investigated causes of body mass loss associated with consecutive days of live trapping of old-field mice (Peromyscus polionotus) on four small mammal trapping grids in central Florida USA from Mar. 2003 to Dec. 2004. Body mass of P. polionotus declined when live trapped for two consecutive days. Mean mass losses were recorded in all seasons and were significantly different in spring and summer. Temperatures inside live traps were higher than ambient temperatures. Mean number of sunflower seeds ingested was not different between day one and day two of capture, and the total number of sunflower seeds consumed explained a small amount of the variation in body mass loss. Our results suggest that sunflower seeds are not a good source of water necessary to maintain a constant body mass in P. polionotus live trapped on consecutive days, and mass loss is influenced by a combination of seasonal temperature fluctuations and physiological condition of trapped individuals.