ABSTRACT: Zooplankton are commonly frozen at sea in ecological studies when it is impractical to extract lipids immediately from live animals. Analysis of lipids extracted from the copepod Calanus pacificus established that freezing has negligible effects oncopepod dry mass, total lipid content, or lipid composition, resulting only in slight changes in free fatty acids. However, storage for 1 yr at -15*C resulted in substantial loss of polar lipids and accumulation of free fatty acids when compared withanimals stored at -80*C. Rapid freezing in liquid nitrogen, followed by maintenance of animals at temperatures below -70*C, is recommended where immediate lipid extraction is not feasible.