Determination of elapsed time since death in small cetaceans can be important to our understanding of the nature of their interactions with fishing operations. This pilot study was conducted to determine the potential diagnostic usefulness of ocular fluid (vitreous humour) and core body temperature to estimate postmortem intervals in harbour porpoises (Phocoena phocoena). Core temperature and concentrations of various constituents of vitreous humour (glucose, urea, sodium, potassium, chloride, magnesium, calcium, and phosphorus) were determined in 24 harbour porpoises incidentally caught in groundfish gillnets in the waters of the Gulf of Maine and the Bay of Fundy. These parameters were compared to published values for rectal temperatures and the serum concentrations of several selected elements in live harbour porpoises. Glucose in vitreous humour decreased in dead animals compared to serum values in live ones; its level was positively correlated with core temperature. Potassium and magnesium in vitreous humour increased following death. These data suggest that most animals analysed had been dead for several hours. For the present, the methodology affords researchers an approach that appears to hold some promise. However, the most practical technique requires testing animals with a known time of death in order to derive a set of curves for ocular fluid values and temperature versus time that are appropriate for a statistical presentation of predictability for the time since death.