Oil-based teat dips containing iodine at .5 and 1% were compared in a series of studies with two water-based iodophor products of the same concentration and also with undipped controls. When the two types of products were tested at .5% under conditions of natural infection, the water-based dip was four times more effective than the oil-based dip at preventing Staphylococcus aureus infections. In three subsequent trials teats were experimentally exposed to S. aureus and Streptococcus agalactiae. Five times more S. aureus infections developed in a group dipped with the oil-based dip at 1% iodine with an undipped control yielded no significant difference for S. aureus infections. The 1% iodine water-based product was nine times more effective in preventing S. aureus infections than the 1% oil-based product. Differences in the incidence of S. agalactiae infections were nonsignificant within the individual trials. Though ineffective in preventing udder infections oil-based products were effective in creating a supple condition of teat skin.