Right flank laparotomies were performed on five clinically healthy cross-bred calves. A significant (P less than 0.05) increase of 22.1 and 2.7 times in bacterial count in subcutaneous tissue and incised skin edges, respectively, and a non-significant increase (1.1 times) in muscles and peritoneum had occurred during 15 minutes exposure to the operation theatre environment. Poly-morphonuclear cells and Gram-positive and Gram-negative bacterial infiltration was also demonstrated histopathologically in muscles and peritoneum. Organisms isolated from operation theatre air were Staphylococcus aureus, other Staphylococcus spp., Bacillus spp., Micrococcus spp., and yeast. Usually similar organisms were also found on the laparotomy wound, just before closure of abdomen. Operation theatre environment is concluded to be a significant source of operative wound contamination. Provision of separate operation theatres for different types of surgery in different species is recommended and the necessity for their regular disinfection is stressed.