An automatic device, which infuses disinfectant into the mouthpiece of the liner of the milking machine cluster as teatcups are removed, is described. Application at this time avoids any delay in disinfection, reduces the workload in the parlour and increases reliability of application. The teats of 20 cows were contaminated before each milking by immersion in a suspension of Staphylococcus aureus and Streptococcus agalactiae and then disinfected manually or automatically with iodophor after milking. Str. agalactiae was recovered from < 5% of swabs and there was no difference between the results from the two methods. Neither method of disinfection was as effective against Staph. aureus and the recovery rate was significantly greater for the automatic method for both swabs from teat barrel (P < 0·05) and teat apex (P < 0·001). Rates of intramammary infection for quarters automatically or manually disinfected were similar and low (3/40 v. 6/40 respectively). The automatic method facilitates cluster removal by relieving vacuum and decreasing frictional contact at the mouthpiece lip, and utilizes approximately half the quantity of disinfectant used by manual dipping (0·9 v. 1·9 ml/teat). However, iodine contamination in the milk from the iodophor teat disinfectant was significantly increased from 14·4 to 102·2 μg I2/100 ml milk when no backflushing was practised.