The purpose of this paper is to give a report of conclusions drawn from the linguistic investigation and dialect intelligibility testing carried . out in the Upper Kinabatangan River area of the Kinabatangan District in the State of Sabah, Malaysia. The work was part of an extensive language survey initiated by the Summer Institute of Linguistics. Due to difficulties of travel and communication, the survey in theKinabatangan District was divided into two phases, the first of which is reported -liere and was carried out by the authors in the Upper Kinabatangan from October 1978 to March 1979