Tissues from fin (Balaenoptera physalus) and sei (Balaenoptera borealis) whales taken off the coast of Southwest Iceland in July–August in 1978 and 1981 were analysed for percent lipid, protein, and ash contents. The tail region of the whales, especially the dorsal area, constituted the main area of lipid storage in both blubber and muscle. No significant differences (p > 0.05, ANOVA) were evident between reproductive classes, except that adult females appear to store more lipid in the tail muscles than other classes. Most sei whale tissues contained more lipid than those of fin whales, but the differences may be explained by variations in seasonal feeding and fattening. Seasonal variations and differences between reproductive classes were evident from girth and blubber thickness. Juvenile males were thinnest and adult females were thickest.
