ABSTRACT NL's Wire Telemetry System was used in the field to provide high-data-rate measurements of downhole forces, accelerations, pressures and formation properties. This paper describes, and briefly discusses, downhole longitudinal and lateral vibrations and their correlation with formation characteristics. Whi1e drilling through hard formations with a tricone bit, smooth drilling was achieved after increasing the rotary speed above the longitudinal resonant condition. The system resonant frequency was significantly lower than the natural frequency of the drillstring. Downhole bending moments up to 25Kft-1b were measured while drilling in a straight hole. Fluctuations in the bending moments, about the two lateral axes of the drillstring, were at frequencies 3.5 to 5.5 times that of the rotary speed.