A method and a device are presented with which an analysis sample of less than 50 ml can be extracted from a milk flow having an amount which is proportional, even for cows having an expected total milk amount of up to 30 kg as well as an expected maximum milk flow of 12 kg per minute. The method is characterized in that by using a valve controlled in cycles, whereby each cycle comprises a valve opening time and a valve closing time, for extracting simply an analysis sample held below a predetermined maximum amount of 50 ml from the expected value of the total milk amount to be milked from the particular cow gained from experience, a cycle time and a valve opening time are determined, whereby the cycle time and the valve opening time are respectively chosen in such a way that they lie within a predetermined range of values, that the valve opening time or the cycle time is controlled in dependence of the milk flow, and that to avoid the values of the valve opening time or the cycle time lying outwith the range of values as a result of a change in the milk flow, the valve opening time and the cycle time are changed in the same proportions to the values lying within the range. The device with which such a milk sample extraction can be carried out with, comprises a milk flow measuring device, a processor unit and a milk sample extracting device which substantially comprises an electrically controllable magnet coil with which a sealing body is moveable to a first position closing the through flow opening for the sample separating stream and a second position releasing this opening.