Clinical biochemistry is the measurement of body fluid constituents, and is considered an integral component of disease diagnosis in human and veterinary medicine. Biochemical reference intervals are the ranges of values of specific analytes at the population level that are expected to encompass 95% of “normal” individuals. However, how do we define a “normal” lobster? Homarus americanus (H. Milne Edwards, 1837) is a sublittoral ectotherm with a limited homeostatic ability to adapt to rapid environmental changes. An experiment was designed to measure the changes that may occur in selected analytes as wild lobsters “acclimate” to captivity. Biological variation was minimized by the maintenance of strict environmental conditions, uniform life stages, nutrition, and molt status. The results of this experiment suggest that elevations in hemolymph levels of glucose, L-lactate, crustacean hyperglycemic hormone, ammonia, ionic calcium, and a decrease in ionic potassium may be indicative of the stress associated with capture, handling, and emersion hypoxia. Although the data demonstrate a considerable intraspecific variation in most analytes during the acclimation process, these reference intervals may be useful in the interpretation of clinical findings in lobsters held in captivity for research or exhibition in public aquaria.