A novel milk sampler (MilkThief) is described. It can collect representative samples of milk to be used for disease monitoring from groups of cows during a milking session. The maximum dilution of each individual cow¿s milk did not exceed a 1 : 45 limit when we tested the sampler in a range of Australian dairies. Such a dilution limit has been shown by others to be efficient for the detection of enzootic bovine leucosis when the `Lactelisa¿ method is used. The samplers and collection flasks are conveniently left in place for the whole milking session. The sampling volume can be manipulated so that the combined sample collected from up to 10 cows can be held in a flask of 220-mL capacity. The sampler can be easily fitted to any milking machine.