Late Pleistocene intermediate water ventilation history in the northeastern Pacific has been inferred from benthic foraminiferal carbon isotopic data from seven California margin basins. Secular variations in oceanic delta (super 13) C recorded at North Pacific ODP Site 849 were subtracted from each basin record leaving a residual delta (super 13) C history that reflects variations in ventilation. During the previous interglacial intermediate waters above 2000 m contained less oxygen than they do today or Pacific deep water at Site 849 was better ventilated. Intermediate water ventilation began to improve during oxygen isotope stage 4 and continued to improve throughout stages 3 and 2. This enhanced ventilation was not contemporaneous at all depths and appears to have progressed upwards through the water column. The diachronous nature of these changes suggest that there was not simply an "on"/"off" mechanism which resulted in higher or lower ventilation in the North Pacific during the last glacial cycle.