We have investigated the content and structure of the chrysolaminarans isolated from the two marine diatoms Chaetoceros mülleri and Thalassiosira weissflogii. Samples were taken from different phases of growth, and the structure of the chrysolaminaran was seen in relation to the specific growth rate of the diatoms. The structure determined for the glucan from C. mülleri was found not to vary with different specific growth rates. T. weissflogii showed some variance in the structure, both throughout the different stages of growth and between samples taken from the stationary phase. C. mülleri was found to have a chrysolaminaran with a degree of polymerization (DP) of 22-24 and a degree of beta-(1-->6) branching of 0.006-0.009. These results corresponded well with previous results obtained in our laboratories. The chrysolaminaran isolated from T. weissflogii was found to have a DP of 5-13 and no beta-(1-->6) branching. This is to our knowledge the first characterization of the chrysolaminaran from T. weissflogii.