Iodine values, Reichert values, saponification values and softening points of butterfats from butters collected at monthly intervals over a period of 4 years from 9 factories representative of the main butter-producing districts in New Zealand were determined. The trend of variation of any one property throughout the season was remarkably uniform, both for different factories in the one season, and for any one property in the four seasons. Weighted monthly average iodine values, Reichert values, saponification values and softening points for the butterfat from all factories over 4 years were 36.7 (33.8–40.2), 30.4 (25.5–32.3), 229.5 (225.5–232.7) and 33.1 (32.2–33.7) respectively. The minimum iodine value occurred in midsummer, i.e. at the season of the year when maximum values are reported for northern hemisphere butters. The iodine values for South Island butterfats diverged markedly from those for the North Island butterfats during the winter, i.e. at the time when turnips are fed to cows in the South. In spite of these lower iodine values, the softening points of the South Island butterfats were lower throughout the year.