Monthly samples of butterfat taken during 1953–54 from creameries at Edmonton and Lethbridge showed regional and seasonal fluctuations of iodine values and content of monoenoic and conjugated and non-conjugated dienoic, trienoic and tetraenoic acids. The total unsaturated acids content, as measured by iodine values, was higher in the Edmonton butterfats and reached a maximum in September at the end of the grazing season, while the lower Lethbridge maximum occurred in May with but slightly declining values throughout the summer. Minimum values were recorded during November and December for both regions. Maximum oleic acid occurrence did not coincide with the peak of the grazing season. Most of the polyunsaturated acids varied seasonally but marked regional differences were not observed. In general the latter constituents occurred in amounts comparable to those reported elsewhere. With the exception of the non-conjugated dienoic acids, summer values were high and winter values low. Conjugated tetraenoic acids were found in all butterfats but in trace amounts only.