A Coulter counter was used to measure the diameters and numbers of fat globules in serial samples taken during a single milking of each of 8 cows. Milk fat percentages of samples were estimated by the Babcock method. The average globule diameter, globule number and fat percentage all increased during milking. Regression analyses indicated that fat percentage was a stronger function of fat globule diameter than of globule number. The results are discussed with relation to the rise in fat percentage that occurs during milking.