We have investigated the responses of cow teats to machine milking in a study of relatively newly installed commercial milking parlours fitted with one of two types of milking cluster. The first was a common type with a large claw volume (> 200 ml), 15–16 mm i.d. long milk tube, 10 mm short pulse tube, cluster weight < 3·2 kg and used alternate pulsation. The second was a more traditional type with a 150 ml claw bowl volume, 13·5 mm i.d. long milk tube, 8 mm short pulse tube, cluster weight ∼ 3·5 kg and used simultaneous pulsation. We scored ∼ 50 cows in each of 20 herds, all within 60 s of cluster removal, for changes from the premilking teat condition: teat colour (creation of reddening or blueness), firmness, thickening at the base of the teat associated with the position of the liner mouthpiece, and whether the teat duct orifice was open. There were statistically significant differences in the proportion of cows displaying these four alterations in teat condition between herds using the two types of cluster. The more common type of cluster was always associated with better teat condition. The cause and effect of poorer teat condition have not been fully established and are likely to be multifactorial. The principal risk factors may be cluster weight, overmilking, vacuum applied during the overmilking phase and the design of the liner mouthpiece.