Poor hatchability can occur due to eggshell bacterial contamination, which can be decreased by UV light or H(2)O(2) alone. However, antimicrobial effects of these 2 treatments combined, as well as optimum length of UV exposure, are not known. Therefore, the objectives of this study were to determine the optimum length of UV exposure for maximum bacterial reduction and to determine if a greater bacterial reduction would occur using a combination of UV and H(2)O(2) compared with either treatment alone. The first experiment was conducted to determine the optimum length of UV exposure by exposing eggs to 4, 8, 16, and 32 min of UV. Three experiments were also conducted to determine what concentration of H(2)O(2) in combination with UV exposure would yield maximum bacterial reduction. For experiment 2, treatments consisted of a control and UV alone as well as 0, 1, 2, and 3% H(2)O(2) alone and in combination with UV for 8 min. In experiment 3, treatments consisted of a control, UV alone, 3% H(2)O(2) alone, as well as 0, 0.5, 1, 1.5, 2, 2.5, and 3% H(2)O(2) in combination with UV for 8 min. Experiment 4 used 10 treatments including a control and 1.5, 2, and 2.5% H(2)O(2) at UV exposure times of 2, 4, and 8 min for each H(2)O(2) concentration. Results indicated that every control eggshell contained bacteria, resulting in an average bacterial count of 4 log cfu/egg. Exposure to UV alone for 8 min yielded significant bacterial reductions without excessive egg heating. When administered independently, H(2)O(2) and UV each reduced eggshell bacterial counts by 2 log cfu/egg. The combination of 1.5% H(2)O(2) and UV for 8 min reduced bacterial counts by a maximum of 3 log cfu/egg, with only 35% of the eggs positive for bacteria. Because bacterial contamination was further reduced by using a combination of UV and H(2)O(2), it is possible that hatchability and chick quality of breeder eggs might be improved by such treatments.