EqPac is the United States-Joint Global Ocean Flux Study (US-JGOFS) process study in the central equatorial Pacific. The first EqPac cruises sailed in January 1992 during a moderately strong El Niño. This was fortuitous for our studies of chemical and biological distributions because El Niño events are difficult to predict, and the lead time for a project of this size is long. There was virtually no previous upper-water-column chemical or biological data for El Niño conditions in the central equatorial Pacific. Now an El Niño has been studied in considerable detail, and it will be easy to sample the extremes in environmental conditions by sampling non-El Niño conditions (including La Niña) in 1993 and the years thereafter. The implementation of EqPac illustrates how difficult it is to mount a large-scale interdisciplinary study of the ocean when the interannual variability is large.