Dive habits of four Northeast Pacific blue whales (Balaenoptera musculus) were studied using satellite-monitored radio tags. Tags summarized dive-duration data into eight 3-h periods daily. One tag additionally summarized dive depth and time-at-depth information for these same periods. Tracking periods ranged from 0.6 to 12.7 d and provided data for 17 three-hour summary periods, representing 2,007 dives (788 of which provided depth information). Total number of dives during a 3-h summary period ranged from 83 to 128. Seventy-two percent of dives were ≤ 1 min long. All whales spent >94% of their time submerged. Average duration of true dives (dives >1 min) ranged from 4.2 to 7.2 min. Seventy-five percent of depth-monitored dives were to ≤16 m, accounting for 78% of that animal's time. Average depth of dives to >16 m was 105 ± 13 m.