Removing milker units as soon as milk flow stopped was compared to milking for a fixed time of 12 min in an 8-wk trial with 60 cows. Teats were dipped in broth culture of approximately 10(9) colony forming units per ml of Staphylococcus aureus, Streptococcus agalactiae, and Streptococcus uberis for 4 wk. More new infections of quarters occurred in the 12-min group. In trials 2 and 3, 20 additional cows were milked with automatic milking machine detachers and 20 cows were milked with a flow control unit for 12 min each trial. New infection rates were highest in the two groups milked for 12 min. Age for lactation and cows were associated with most of the variation in the new infection rate. Cows with pointed teat ends had the highest rate of new infection. Effects of fixed-time milking on increased mammary infection and clinical mastitis were small.