The biochemical composition of juvenile blue crabs, Callinectes sapidus, exposed to sublethal concentrations of the water-soluble fraction of South Louisiana crude oil (0 to 2 504 ppb) for 21 d were examined. Although growth took place in all crabs, tissue content varied inversely with exposure concentration while percentage tissue water varied directly with exposure concentration. Total protein, lipid and RNA content of crabs exposed to crude oil were significantly less than that of control crabs by Day 21. DNA content was not significantly different from that of control crabs, suggesting that the difference in tissue content was due to differences in cell volume and not cell number. There were no consistent differences in the concentration of the major biochemical components, indicating that the relative contribution of each of the components remained stable during the period of sublethal stress. Ratios of RNA:DNA and protein:DNA decreased in exposed crabs and were positively correlated with scope for growth and observed growth. The ratios may be useful as indirect indicators of physiological condition. Analysis of lipid classes indicated that structural lipids in stressed crabs were less affected than were lipids used for energy storage. The changes in biochemical composition suggest that the pattern of energy utilization was altered in crabs exposed to crude oil. Growth in size without comparable growth in tissue resulted in decreased tissue content. Available energy was used for growth, with little being stored in lipid reserves. 1986) and growth (Bulow et al. 1978, Dortch et al. 1983, Buckley 1984). Another objective of the present study was to determine whether changes in nucleic acid and protein to DNA ratios have a bioenergetic basis and whether they can be used as indicators of stress in organisms exposed to pollutant stress.