Palaeomagnetic measurements of the polarity of sediments from the Koobi Fora Formation [Pliocene, Pleistocene] east of Lake Rudolf provide a valuable check on other dating methods and allow a polarity stratigraphy to be suggested for the Formation. [These measurements are compared to a chronology by Maglio based on the fossil fauna, including Mesochoerus limnetes, Metridiochoerus andrewsi and Loxodonta africana.].