Two germicides, one containing 0.5% chlorhexidine and one containing 1% iodine, were tested for efficacy against new intramammary infections (IMI) caused by Staphylococcus aureus and Streptococcus agalactiae. The model for the experimental challenge in the trials that were designed to test the efficacy of the two postmilking teat dips was recommended by the National Mastitis Council. The 0.5% chlorhexidine product reduced the number of new IMI caused by Staph. aureus by 73.2% and reduced the number of new IMI caused by Strep. agalactiae by 53.9%. The 1% iodine product reduced the number of new IMI caused by Staph. aureus by 75.6% and reduced the number of new IMI caused by Strep. agalactiae by 53.5%. In both trials, the incidence of clinical mastitis was also reduced in dipped quarters compared with control quarters. Use of the two teat dips over the trial periods had no effect on the condition of teat skin or teat ends.