Specimens of harbour porpoises, Phocoena phocoena, from both strandings and bycatch in fisheries around the United Kingdom between 1985 and 1994 have been examined. Full autopsies were undertaken on most carcases, and measurements and samples taken. The sex, date of finding, location, total body length, girth, body and organ weights, blubber thicknesses and blubber samples, reproductive organs and teeth were all collected during this period. A total sample of 303 individuals (including 144 males + 128 females), with data on most parameters, has been analysed. Small juvenile animals are both relatively and actually fatter than adults. The latter point may reflect the greater surface/volume ratios of young and their need for insulation. Blubber thickness and body size may also be important in thermoregulation for all animals. Length, cm (L) and mid-girth, cm (G) together provide the means of most accurate estimation of body weight, kg (W) for both sexes:
W = 0.000081.L^(1.2401).G^1.5524.
Limited female data indicate that pregnant females are heavier and fatter, and that lactating females are lighter and leaner than anoestrous females. Blubber lipid content, determined from the blubber samples, averaged 83-87% wet weight tissue for all classes of animals except neonates (^90cm), which appeared in the samples mainly during June and had a lower mean of about 68% wet weight tissue.