External otitis has been associated with wearing obstructive gear covering the earlobe and external ear canal. In this study we investigated the changes in the bacterial flora of the external ear canal after wearing rubber hoods. The bacterial flora of external ear canals surfaces was investigated in a group of 19 volunteers who wore rubber hoods for a period of 25 to 30 minutes while doing manual work. The protective effect of 2% acetic acid was tested by instilling it in the left ear of all participants. Staphylococcus epidermidis, Propionibacterium acnes, and alpha-hemolytic streptococci were the predominant isolates from the ear samples. After hoods were worn, there was a substantial increase in the number of these organisms in 7 (36.8%) of the external ears. However, an increase in the bacterial counts in the external ear canals occurred in only 2 (10.5%) of the individuals treated prophylactically with acetic acid drops (P less than 0.02).