Concentrations and activities of selected biochemicals of loggerhead sea turtles (Caretta caretta) were determined for plasma that was separated from whole blood samples that were kept up to 96 hr post collection (PC) in a refrigerator. Blood samples collected from seven juvenile captive loggerhead sea turtles were added to tubes containing lithium heparin and were placed on ice. Equal amounts of anticoagulated whole blood from the lithium heparin tubes were then aliquoted into plastic tubes and stored as whole blood under refrigeration until they were centrifuged at 0, 4, 24, 48, and 96 hr PC. Plasma was removed and the analytes that were measured were alkaline phosphatase (ALP), aspartate aminotransferase (AST), gamma glutamyl transferase (GGT), creatine kinase (CK), sodium, chloride, potassium, magnesium, calcium, phosphorus, cholesterol, glucose, urea nitrogen, uric acid, total protein, albumin, and globulin. Compared with values at 0 time, the only analyte to be significantly different at 24 hr PC was GGT (activity decreased by 25%). Compared with values at 0 time, significant differences at 96 hr PC were only seen in AST (2% increase), GGT (25% decrease), glucose (7% decrease), and uric acid (25% increase). Although a statistically significant difference was found in concentrations of phosphorus and cholesterol over time by repeated measures analysis of variance (ANOVA), the follow-up multiple comparison procedure could not define the specific time points at which significant differences occurred. For all other analytes, significant differences over the time course of the study were not found. In these instances, the power of the ANOVA was sufficient (≥0.80) to detect any arithmetic differences of a clinically relevant magnitude. Although plasma should be separated from the cellular component of blood as soon as possible PC, in a field situation in which a centrifuge is unavailable, samples can be stored in a portable cooler up to 24 hr without appreciable change in select biochemical analytes.