The objective of this study was to investigate the influence of enrofloxacin (ENR) traces on doxycycline (DC) pharmacokinetic depletion phase parameters in plasma and lungs of healthy and Mycoplasma gallisepticum (MG)-infected chicken broilers. The multiple-dose oral administration of DC to chickens which were permanently exposed on ENR traces significantly increased concentration of DC in plasma and lung. It also prolonged the DC elimination time in both healthy and infected animals after final dose. The obtained result indicated that simultaneous administration of DC and ENR in chicken broilers therapy should be avoided.