Time variations of the Pacific equatorial undercurrent at 150° west longitude are described, based upon observations from the CSS Parizeau during January-February 1979. Typical velocity maxima were 80 cm s⁻¹ in the eastward direction and 60 cm s⁻¹ in the northward direction near the core depth at 150 metres. Associated standard errors were 15 cm s⁻¹ due to uncertainty in probe motion and 5 cm s⁻¹ due to inherent current meter noise. Scalar field analysis suggests that the mean zonal current flow in the equatorial undercurrent is modulated by Rossby waves with periods of 30 days. In the surface layer, waves with periods of approximately 17 days were detected. A detailed description of the current profiler used during the experiment is included in the Appendix. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate