Previous work established that the serum protein concentration of lobster hemolymph was a valid index of the amount of muscle in the live lobster and its measurement provided a rapid non-destructive determination of the animal's physical condition. This measurement has been applied to slightly more than 1000 adult lobsters captured from widely separated locations in the Canadian Atlantic littoral to determine their physical condition throughout the annual cycle. A statistical analysis of these data was performed.The recovery of serum protein concentrations from the low levels following ecdysis, in all areas, was rapid initially, and appeared to be arrested during the winter. It was completed rapidly during the spring-summer warming period, culminating again in ecdysis. The maximal and minimal serum protein concentrations and their rate of change were quite different in the different areas. The results show clearly that the characteristics of the annual cycle for an area were unique to that area. The effect of temperature was considered as well as the effect of the long-term cooling trend in the northwestern Atlantic. The importance of the possibility of the observed differences being genetically fixed was discussed. The overall method would appear to afford a good, rapid means for studying the impact of the entire environment on the lobster as well as supplying information on the environment itself on which to base management practices and the selection of experimental animals.